[1.2.X] Fixed a number of tests that were failing in Oracle due to false...

[1.2.X] Fixed a number of tests that were failing in Oracle due to false assumptions about the primary keys of objects.
Backport of r15779 from trunk.

git-svn-id: http://code.djangoproject.com/svn/django/branches/releases/1.2.X@15780 bcc190cf-cafb-0310-a4f2-bffc1f526a37