Added passing unit test (for initial AuthResponse) and failing unit test (for subsequent AuthResponses).
Merge pull request #397 from Its-Tyson/email-based-username-authresponse-issue

Issue with missing AuthResponse.Username value when using email based usernames
Added code documentation to warn about the session changing side effects.
Merge branch 'master' into html-auth-session-referrer-workaround

Conflicts:
	tests/ServiceStack.WebHost.Endpoints.Tests/AuthTests.cs