如何解决NuGet.exe命令行无法安装xunit 2.1.0的问题

使用更新5和NuGet Package Manager 2.8.60610.756在Visual Studio 2013中创建一个全新的项目可以完美地安装xunit 2.1.0

------- Installing...xunit 2.1.0 -------
Attempting to resolve dependency 'xunit.core (= 2.1.0)'.
Attempting to resolve dependency 'xunit.extensibility.core (= 2.1.0)'.
Attempting to resolve dependency 'xunit.abstractions (= 2.0.0)'.
Attempting to resolve dependency 'xunit.extensibility.execution (= 2.1.0)'.
Attempting to resolve dependency 'xunit.assert (= 2.1.0)'.
Installing 'xunit.abstractions 2.0.0'.
Added file 'xunit.abstractions.dll' to folder 'xunit.abstractions.2.0.0'lib'net35'.
Added file 'xunit.abstractions.xml' to folder 'xunit.abstractions.2.0.0'lib'net35'.
Added file 'xunit.abstractions.dll' to folder 'xunit.abstractions.2.0.0'lib'portable-net45+win+wpa81+wp80+monotouch+monoandroid+Xamarin.iOS'.
Added file 'xunit.abstractions.xml' to folder 'xunit.abstractions.2.0.0'lib'portable-net45+win+wpa81+wp80+monotouch+monoandroid+Xamarin.iOS'.
Added file 'xunit.abstractions.2.0.0.nupkg' to folder 'xunit.abstractions.2.0.0'.
Successfully installed 'xunit.abstractions 2.0.0'.
Installing 'xunit.extensibility.core 2.1.0'.
Added file 'xunit.core.dll' to folder 'xunit.extensibility.core.2.1.0'lib'dotnet'.
Added file 'xunit.core.dll.tdnet' to folder 'xunit.extensibility.core.2.1.0'lib'dotnet'.
Added file 'xunit.core.pdb' to folder 'xunit.extensibility.core.2.1.0'lib'dotnet'.
Added file 'xunit.core.xml' to folder 'xunit.extensibility.core.2.1.0'lib'dotnet'.
Added file 'xunit.runner.tdnet.dll' to folder 'xunit.extensibility.core.2.1.0'lib'dotnet'.
Added file 'xunit.runner.utility.desktop.dll' to folder 'xunit.extensibility.core.2.1.0'lib'dotnet'.
Added file 'xunit.core.dll' to folder 'xunit.extensibility.core.2.1.0'lib'portable-net45+win8+wp8+wpa81'.
Added file 'xunit.core.dll.tdnet' to folder 'xunit.extensibility.core.2.1.0'lib'portable-net45+win8+wp8+wpa81'.
Added file 'xunit.core.pdb' to folder 'xunit.extensibility.core.2.1.0'lib'portable-net45+win8+wp8+wpa81'.
Added file 'xunit.core.xml' to folder 'xunit.extensibility.core.2.1.0'lib'portable-net45+win8+wp8+wpa81'.
Added file 'xunit.runner.tdnet.dll' to folder 'xunit.extensibility.core.2.1.0'lib'portable-net45+win8+wp8+wpa81'.
Added file 'xunit.runner.utility.desktop.dll' to folder 'xunit.extensibility.core.2.1.0'lib'portable-net45+win8+wp8+wpa81'.
Added file 'xunit.extensibility.core.2.1.0.nupkg' to folder 'xunit.extensibility.core.2.1.0'.
Successfully installed 'xunit.extensibility.core 2.1.0'.
Installing 'xunit.extensibility.execution 2.1.0'.
Added file 'xunit.execution.dotnet.dll' to folder 'xunit.extensibility.execution.2.1.0'lib'dnx451'.
Added file 'xunit.execution.dotnet.pdb' to folder 'xunit.extensibility.execution.2.1.0'lib'dnx451'.
Added file 'xunit.execution.dotnet.xml' to folder 'xunit.extensibility.execution.2.1.0'lib'dnx451'.
Added file 'xunit.execution.dotnet.dll' to folder 'xunit.extensibility.execution.2.1.0'lib'dotnet'.
Added file 'xunit.execution.dotnet.pdb' to folder 'xunit.extensibility.execution.2.1.0'lib'dotnet'.
Added file 'xunit.execution.dotnet.xml' to folder 'xunit.extensibility.execution.2.1.0'lib'dotnet'.
Added file 'xunit.execution.dotnet.dll' to folder 'xunit.extensibility.execution.2.1.0'lib'monoandroid'.
Added file 'xunit.execution.dotnet.pdb' to folder 'xunit.extensibility.execution.2.1.0'lib'monoandroid'.
Added file 'xunit.execution.dotnet.xml' to folder 'xunit.extensibility.execution.2.1.0'lib'monoandroid'.
Added file 'xunit.execution.dotnet.dll' to folder 'xunit.extensibility.execution.2.1.0'lib'monotouch'.
Added file 'xunit.execution.dotnet.pdb' to folder 'xunit.extensibility.execution.2.1.0'lib'monotouch'.
Added file 'xunit.execution.dotnet.xml' to folder 'xunit.extensibility.execution.2.1.0'lib'monotouch'.
Added file 'xunit.execution.desktop.dll' to folder 'xunit.extensibility.execution.2.1.0'lib'net45'.
Added file 'xunit.execution.desktop.pdb' to folder 'xunit.extensibility.execution.2.1.0'lib'net45'.
Added file 'xunit.execution.desktop.xml' to folder 'xunit.extensibility.execution.2.1.0'lib'net45'.
Added file 'xunit.execution.dotnet.dll' to folder 'xunit.extensibility.execution.2.1.0'lib'portable-net45+win8+wp8+wpa81'.
Added file 'xunit.execution.dotnet.pdb' to folder 'xunit.extensibility.execution.2.1.0'lib'portable-net45+win8+wp8+wpa81'.
Added file 'xunit.execution.dotnet.xml' to folder 'xunit.extensibility.execution.2.1.0'lib'portable-net45+win8+wp8+wpa81'.
Added file 'xunit.execution.dotnet.dll' to folder 'xunit.extensibility.execution.2.1.0'lib'win8'.
Added file 'xunit.execution.dotnet.pdb' to folder 'xunit.extensibility.execution.2.1.0'lib'win8'.
Added file 'xunit.execution.dotnet.xml' to folder 'xunit.extensibility.execution.2.1.0'lib'win8'.
Added file 'xunit.execution.dotnet.dll' to folder 'xunit.extensibility.execution.2.1.0'lib'wp8'.
Added file 'xunit.execution.dotnet.pdb' to folder 'xunit.extensibility.execution.2.1.0'lib'wp8'.
Added file 'xunit.execution.dotnet.xml' to folder 'xunit.extensibility.execution.2.1.0'lib'wp8'.
Added file 'xunit.execution.dotnet.dll' to folder 'xunit.extensibility.execution.2.1.0'lib'wpa81'.
Added file 'xunit.execution.dotnet.pdb' to folder 'xunit.extensibility.execution.2.1.0'lib'wpa81'.
Added file 'xunit.execution.dotnet.xml' to folder 'xunit.extensibility.execution.2.1.0'lib'wpa81'.
Added file 'xunit.execution.dotnet.dll' to folder 'xunit.extensibility.execution.2.1.0'lib'xamarinios'.
Added file 'xunit.execution.dotnet.pdb' to folder 'xunit.extensibility.execution.2.1.0'lib'xamarinios'.
Added file 'xunit.execution.dotnet.xml' to folder 'xunit.extensibility.execution.2.1.0'lib'xamarinios'.
Added file 'xunit.extensibility.execution.2.1.0.nupkg' to folder 'xunit.extensibility.execution.2.1.0'.
Successfully installed 'xunit.extensibility.execution 2.1.0'.
Installing 'xunit.core 2.1.0'.
Added file '_._' to folder 'xunit.core.2.1.0'build'dnx451'.
Added file '_._' to folder 'xunit.core.2.1.0'build'monoandroid'.
Added file '_._' to folder 'xunit.core.2.1.0'build'monotouch'.
Added file '_._' to folder 'xunit.core.2.1.0'build'net45'.
Added file 'xunit.core.props' to folder 'xunit.core.2.1.0'build'portable-net45+win8+wp8+wpa81'.
Added file '_._' to folder 'xunit.core.2.1.0'build'win8'.
Added file 'xunit.core.props' to folder 'xunit.core.2.1.0'build'win81'.
Added file '_._' to folder 'xunit.core.2.1.0'build'wp8'.
Added file 'xunit.core.props' to folder 'xunit.core.2.1.0'build'wpa81'.
Added file '_._' to folder 'xunit.core.2.1.0'build'xamarinios'.
Added file 'xunit.execution.desktop.dll' to folder 'xunit.core.2.1.0'build'_desktop'.
Added file 'xunit.core.2.1.0.nupkg' to folder 'xunit.core.2.1.0'.
Successfully installed 'xunit.core 2.1.0'.
Installing 'xunit.assert 2.1.0'.
Added file 'xunit.assert.dll' to folder 'xunit.assert.2.1.0'lib'dotnet'.
Added file 'xunit.assert.pdb' to folder 'xunit.assert.2.1.0'lib'dotnet'.
Added file 'xunit.assert.xml' to folder 'xunit.assert.2.1.0'lib'dotnet'.
Added file 'xunit.assert.dll' to folder 'xunit.assert.2.1.0'lib'portable-net45+win8+wp8+wpa81'.
Added file 'xunit.assert.pdb' to folder 'xunit.assert.2.1.0'lib'portable-net45+win8+wp8+wpa81'.
Added file 'xunit.assert.xml' to folder 'xunit.assert.2.1.0'lib'portable-net45+win8+wp8+wpa81'.
Added file 'xunit.assert.2.1.0.nupkg' to folder 'xunit.assert.2.1.0'.
Successfully installed 'xunit.assert 2.1.0'.
Installing 'xunit 2.1.0'.
Added file 'xunit.2.1.0.nupkg' to folder 'xunit.2.1.0'.
Successfully installed 'xunit 2.1.0'.
Adding 'xunit.abstractions 2.0.0' to ClassLibrary1.
For adding package 'xunit.abstractions 2.0.0' to project 'ClassLibrary1' that targets 'net45',
>> Assembly references are being added from 'lib'net35'
Added reference 'xunit.abstractions' to project 'ClassLibrary1'
Added file 'packages.config'.
Added file 'packages.config' to project 'ClassLibrary1'
Successfully added 'xunit.abstractions 2.0.0' to ClassLibrary1.
Adding 'xunit.extensibility.core 2.1.0' to ClassLibrary1.
For adding package 'xunit.extensibility.core 2.1.0' to project 'ClassLibrary1' that targets 'net45',
>> Assembly references are being added from 'lib'portable-net45+win8+wp8+wpa81'
Added reference 'xunit.core' to project 'ClassLibrary1'
Added file 'packages.config'.
Successfully added 'xunit.extensibility.core 2.1.0' to ClassLibrary1.
Adding 'xunit.extensibility.execution 2.1.0' to ClassLibrary1.
For adding package 'xunit.extensibility.execution 2.1.0' to project 'ClassLibrary1' that targets 'net45',
>> Assembly references are being added from 'lib'net45'
Added reference 'xunit.execution.desktop' to project 'ClassLibrary1'
Added file 'packages.config'.
Successfully added 'xunit.extensibility.execution 2.1.0' to ClassLibrary1.
Adding 'xunit.core 2.1.0' to ClassLibrary1.
For adding package 'xunit.core 2.1.0' to project 'ClassLibrary1' that targets 'net45',
>> Build files are being added from 'build'portable-net45+win8+wp8+wpa81'
Added file 'packages.config'.
Successfully added 'xunit.core 2.1.0' to ClassLibrary1.
Adding 'xunit.assert 2.1.0' to ClassLibrary1.
For adding package 'xunit.assert 2.1.0' to project 'ClassLibrary1' that targets 'net45',
>> Assembly references are being added from 'lib'portable-net45+win8+wp8+wpa81'
Added reference 'xunit.assert' to project 'ClassLibrary1'
Added file 'packages.config'.
Successfully added 'xunit.assert 2.1.0' to ClassLibrary1.
Adding 'xunit 2.1.0' to ClassLibrary1.
Added file 'packages.config'.
Successfully added 'xunit 2.1.0' to ClassLibrary1.
==============================

使用最新的NuGet命令行exe（2.8.60717.93）执行相同的安装步骤失败，说明它需要NuGet 3.0…

C:'development'tools'nuget> nuget update -self
Checking for updates from https://www.nuget.org/api/v2/.
Currently running NuGet.exe 2.8.6.
NuGet.exe is up to date.
C:'development'tools'nuget> nuget
NuGet Version: 2.8.60717.93
usage: NuGet <command> [args] [options]
Type 'NuGet help <command>' for help on a specific command.
Available commands:
 config      Gets or sets NuGet config values.
 delete      Deletes a package from the server.
 help (?)    Displays general help information and help information about other commands
             .
 install     Installs a package using the specified sources. If no sources are specified
             , all sources defined in the NuGet configuration file are used. If the conf
             iguration file specifies no sources, uses the default NuGet feed.
 list        Displays a list of packages from a given source. If no sources are specifie
             d, all sources defined in %AppData%'NuGet'NuGet.config are used. If NuGet.c
             onfig specifies no sources, uses the default NuGet feed.
 pack        Creates a NuGet package based on the specified nuspec or project file.
 push        Pushes a package to the server and publishes it.
             NuGet's default configuration is obtained by loading %AppData%'NuGet'NuGet.
             config, then loading any nuget.config or .nuget'nuget.config starting from
             root of drive and ending in current directory.
 restore     Restores NuGet packages.
 setApiKey   Saves an API key for a given server URL. When no URL is provided API key is
             saved for the NuGet gallery.
 sources     Provides the ability to manage list of sources located in %AppData%'NuGet'N
             uGet.config
 spec        Generates a nuspec for a new package. If this command is run in the same fo
             lder as a project file (.csproj, .vbproj, .fsproj), it will create a tokeni
             zed nuspec file.
 update      Update packages to latest available versions. This command also updates NuG
             et.exe itself.
For more information, visit http://docs.nuget.org/docs/reference/command-line-reference
C:'development'tools'nuget> nuget install xunit -version 2.1.0
Attempting to resolve dependency 'xunit.core (= 2.1.0)'.
Attempting to resolve dependency 'xunit.extensibility.core (= 2.1.0)'.
Attempting to resolve dependency 'xunit.abstractions (= 2.0.0)'.
Attempting to resolve dependency 'xunit.extensibility.execution (= 2.1.0)'.
Attempting to resolve dependency 'System.Collections (= 4.0.0)'.
Attempting to resolve dependency 'System.Runtime (= 4.0.0)'.
Attempting to resolve dependency 'System.Diagnostics.Debug (= 4.0.0)'.
Attempting to resolve dependency 'System.Globalization (= 4.0.0)'.
Attempting to resolve dependency 'System.IO (= 4.0.0)'.
Attempting to resolve dependency 'System.Text.Encoding (= 4.0.0)'.
Attempting to resolve dependency 'System.Threading.Tasks (= 4.0.0)'.
Attempting to resolve dependency 'System.Linq (= 4.0.0)'.
The 'System.Linq 4.0.0' package requires NuGet client version '3.0' or above, but the current NuGet version is '2.8.60717.93'.
C:'development'tools'nuget>

Visual Studio根本没有提到系统库，并且使用VS2013"启用NuGet-Package还原"也可用于还原包及其依赖项，并且正在运行相同版本的NuGet.exe命令行