Fixed #8059 -- Added additional clarification to the ordering of Memberships...

Fixed #8059 -- Added additional clarification to the ordering of Memberships so that output order is predictable in tests. Thanks to ramiro for the report and fix.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@8166 bcc190cf-cafb-0310-a4f2-bffc1f526a37