Flush csproj noise
Add support for authenticated proxies
Use .Create as .CreateHttp is PCL specific in .NET4
Revert "Use .Create as .CreateHttp is PCL specific in .NET4"

This reverts commit 3f2694099e0ed59963d655595cae6f8fc1832e4c.
Use .Create instead of .CreateHttp as the latter is PCL-only.