[Slightly OT...] Fixed very minor spelling error.
Added TODO which someone could (and perhaps should) look into at some point.
Added support for custom AuthenticationSchemes, to be able to test the upcoming Windows Authentication support.
Faking "after-the-fact" testing to look more TDD than it actually was. ;) Added a new IRestRequest & RestRequst UseDefaultCredentials property, which does what its name implies.
Implemented the support for UseDefaultCredentials in the various layers involved. Note that the integration tests currently only tests the Http.Sync.cs implementation - an async test could also be added if needed.
Fixed whitespace... Was spaces by mistake.
Merge pull request #455 from ecraft/CustomUseDefaultCredentials

Added support for UseDefaultCredentials