[1.3.X] Ensured that some staticfiles tests get properly cleaned up on...

[1.3.X] Ensured that some staticfiles tests get properly cleaned up on teardown. Thanks to Claude Paroz for the patch.

Backport of r17747 from trunk.

git-svn-id: http://code.djangoproject.com/svn/django/branches/releases/1.3.X@17748 bcc190cf-cafb-0310-a4f2-bffc1f526a37