我如何安装microt.net . http通过Nuget到Xamarin.窗体PCL项目

由于System.Net.HttpClient在可移植类库中不可访问，我试图从Nuget安装Microsoft.Net.Http包到HelloWorld Xamarin。窗体PCL项目在Xamarin Studio，但它总是失败与此错误:

Could not install package 'Microsoft.Net.Http 2.0.20710.0'. You are trying to install this package into a project that targets 'portable-net45+wp80+MonoAndroid10+MonoTouch10', but the package does not contain any assembly references or content files that are compatible with that framework. For more information, contact the package author.

根据项目的Nuget页面，它确实支持pcl。