Fixed #14458 -- converted m2m_regress tests from doctests to unittests. We...

Fixed #14458 -- converted m2m_regress tests from doctests to unittests.  We have always been at war with doctests.  Thanks to Gabriel Hurley for the patch.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@14205 bcc190cf-cafb-0310-a4f2-bffc1f526a37