[1.1.X] Fixed #13035 - Incorrect documentation regarding admin and default managers

  
Thanks to rasca for report and gabrielhurley for patch.

Backport of r12930 from trunk


git-svn-id: http://code.djangoproject.com/svn/django/branches/releases/1.1.X@12931 bcc190cf-cafb-0310-a4f2-bffc1f526a37