Edge cases for effective_principals with groupfinder.

* Do not return Authenticated when authenticated userid is None due to
  groupfinder returning None.

* Call groupfinder with authenticated userid not unauthenticated
  userid.
Merge remote-tracking branch 'origin/master'
Add Laurence Rowe to contributors.
Merge pull request #3 from lrowe/master

Edge cases for effective_principals with groupfinder.