[1.0.X]: Fixed #9978 -- Fixed a KeyError exception that was being raised when...

[1.0.X]: Fixed #9978 -- Fixed a KeyError exception that was being raised when using the logout method on the test client on an unauthenticated user, based on patch from ericholscher.

Backport of r10228 from trunk.


git-svn-id: http://code.djangoproject.com/svn/django/branches/releases/1.0.X@10236 bcc190cf-cafb-0310-a4f2-bffc1f526a37