Added our own rmtree error handler to make sure we can delete correctly delete...

Added our own rmtree error handler to make sure we can delete correctly delete .svn directories when running the tests on Windows which are read-only for some reason.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@15120 bcc190cf-cafb-0310-a4f2-bffc1f526a37