Fixed #11042 -- Corrected admin inlines for inherited models. Thanks to...

Fixed #11042 -- Corrected admin inlines for inherited models. Thanks to jsmullyan for the report, and mir for helpful triage work. Patch includes regression test for #8093, and a commented out test for #10992.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@10725 bcc190cf-cafb-0310-a4f2-bffc1f526a37