[1.1.X] Fixed #12837 -- Clarified the naming strategy for m2m intermediate...

[1.1.X] Fixed #12837 -- Clarified the naming strategy for m2m intermediate tables. Thanks to Ramiro Morales for the report and patch.

Backport of r12516 from trunk.

git-svn-id: http://code.djangoproject.com/svn/django/branches/releases/1.1.X@12521 bcc190cf-cafb-0310-a4f2-bffc1f526a37