[1.0.X] Fixed #10785 -- Corrected a case for foreign key lookup where the...

[1.0.X] Fixed #10785 -- Corrected a case for foreign key lookup where the related object is a custom primary key. Thanks to Alex Gaynor for the patch.

Merge of r10952 from trunk.


git-svn-id: http://code.djangoproject.com/svn/django/branches/releases/1.0.X@10953 bcc190cf-cafb-0310-a4f2-bffc1f526a37