This *is* backwards compatible, but `admin.site.root()` has been deprecated. The new style is `('^admin/', include(admin.site.urls))`; users will need to update their code to take advantage of the new customizable admin URLs.

Thanks to Alex Gaynor.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@9739 bcc190cf-cafb-0310-a4f2-bffc1f526a37