[1.0.X] Fixed #7510: the ModelAdmin now uses `self.queryset` instead of the...

[1.0.X] Fixed #7510: the ModelAdmin now uses `self.queryset` instead of the default manager. Thanks, Alex Gaynor. Backport of r10314 from trunk.

git-svn-id: http://code.djangoproject.com/svn/django/branches/releases/1.0.X@10320 bcc190cf-cafb-0310-a4f2-bffc1f526a37