Added NuGet RemoveSource & sensitive source tests
Now testing source is redacted in arguments by RenderSafe() when
IsSensitiveSource = true
Added tests for the RemoveSource method
Added support in fixture for correct GetStandardOutput() output
when sourceExists is specified.
Merge https://github.com/cake-build/cake into nugetsourcetests
Merge pull request #126 from devlead/nugetsourcetests

Added tests for NuGet RemoveSource and sensitive sources.