Fixed #3505 -- Added handling for the error raised when the user forgets the comma in a single element tuple when defining AUTHENTICATION_BACKENDS. Thanks for the help identifying this problem, Mario Gonzalez <gonzalemario@gmail.com>.


git-svn-id: http://code.djangoproject.com/svn/django/trunk@5678 bcc190cf-cafb-0310-a4f2-bffc1f526a37