Fixed #11226 -- Corrected an validation edge case with m2m relations between...

Fixed #11226 -- Corrected an validation edge case with m2m relations between two models with the same class name. Thanks to pkoch for the report, and to Ramiro Morales for the patch.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@12489 bcc190cf-cafb-0310-a4f2-bffc1f526a37