Fixed #10395 -- Fixed more fallout from r9945.

(Simultaneously, stop django.contrib.gis using some internal attribute when
there's a perfectly good public property available to do the same thing.)

git-svn-id: http://code.djangoproject.com/svn/django/trunk@9960 bcc190cf-cafb-0310-a4f2-bffc1f526a37