Fixed #15816 -- Changed docs/ref/utils.txt to refer to django.utils.datastructures instead of just SortedDict. The other stuff is still undocumented, which is probably a good thing

git-svn-id: http://code.djangoproject.com/svn/django/trunk@16036 bcc190cf-cafb-0310-a4f2-bffc1f526a37