[1.0.X] Fixed #8882 -- When a foreign key is among the unique_together fields...

[1.0.X] Fixed #8882 -- When a foreign key is among the unique_together fields in an inline formset properly handle it.

Backport of r9297 from trunk.

git-svn-id: http://code.djangoproject.com/svn/django/branches/releases/1.0.X@9298 bcc190cf-cafb-0310-a4f2-bffc1f526a37