Fixed #12749 -- Corrected a problem with validation of inline primary keys....

Fixed #12749 -- Corrected a problem with validation of inline primary keys. Thanks to Chris.Wesseling@cwi.nl for the report, and nessita for the test case.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@13034 bcc190cf-cafb-0310-a4f2-bffc1f526a37