Fixed #15016 -- Ensured that the messages tests are isolated from local...

Fixed #15016 -- Ensured that the messages tests are isolated from local template directories. Thanks to Gabriel Hurley for the report and patch.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@15407 bcc190cf-cafb-0310-a4f2-bffc1f526a37