Refactored Django's comment system.

Much of this work was done by Thejaswi Puthraya as part of Google's Summer of Code project; much thanks to him for the work, and to them for the program.

This is a backwards-incompatible change; see the upgrading guide in docs/ref/contrib/comments/upgrade.txt for instructions if you were using the old comments system.


git-svn-id: http://code.djangoproject.com/svn/django/trunk@8557 bcc190cf-cafb-0310-a4f2-bffc1f526a37