Fixed #12577. Reverted some changes from [12098] since [12206] made them...

Fixed #12577. Reverted some changes from [12098] since [12206] made them unneccessary. Also, added a test for using generic inlines with unique_together. Thanks for the report, Raffaele Salmaso.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@12268 bcc190cf-cafb-0310-a4f2-bffc1f526a37