[1.1.X] Really this time -- fixed #12721: Ensured objects with generic...

[1.1.X] Really this time -- fixed #12721: Ensured objects with generic relations that use non-integer object ID fields can be deleted on PostgreSQL. Thanks much carljm for patch and Russ for review. 

Remainder of r12353 from trunk, previous attempt only picked up the new tests.



git-svn-id: http://code.djangoproject.com/svn/django/branches/releases/1.1.X@12356 bcc190cf-cafb-0310-a4f2-bffc1f526a37