Fixed #1390 -- Added an app index in the admin interface. Thanks juliae and...

Fixed #1390 -- Added an app index in the admin interface. Thanks juliae and ext for their work on patches.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@8474 bcc190cf-cafb-0310-a4f2-bffc1f526a37