[1.1.X] Fixed #13389 -- Ensured that the app_loading test clears out the app...

[1.1.X] Fixed #13389 -- Ensured that the app_loading test clears out the app cache at the end of each test, so that it doesn't interact badly with flush and other introspected database commands. Thanks to Karen for the report, and Ramiro Morales for the debugging hints.

Backport of r13011 from trunk.

git-svn-id: http://code.djangoproject.com/svn/django/branches/releases/1.1.X@13012 bcc190cf-cafb-0310-a4f2-bffc1f526a37