Modified tests introduced in r15452 to not run 31 test cases twice. Thanks...

Modified tests introduced in r15452 to not run 31 test cases twice. Thanks Julien for discovering this.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@17592 bcc190cf-cafb-0310-a4f2-bffc1f526a37