[1.1.X] Fixed #9674 - documented app_label.

Thanks to andymckay for the report and jpaulett for the patch.

Backport for [11596] from trunk.


git-svn-id: http://code.djangoproject.com/svn/django/branches/releases/1.1.X@11597 bcc190cf-cafb-0310-a4f2-bffc1f526a37