[1.1.X] Fixed #12721: Ensured objects with generic relations that use...

[1.1.X] 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. 

r12353 from trunk.


git-svn-id: http://code.djangoproject.com/svn/django/branches/releases/1.1.X@12355 bcc190cf-cafb-0310-a4f2-bffc1f526a37