[1.2.X] Fixed #15243 -- More clearly document that the transaction functions...

[1.2.X] Fixed #15243 -- More clearly document that the transaction functions needs to be called with a using parameter to work with a non-default database.  Thanks to Jason Kotenko for the patch.  Backport of [15489].

git-svn-id: http://code.djangoproject.com/svn/django/branches/releases/1.2.X@15490 bcc190cf-cafb-0310-a4f2-bffc1f526a37