Fixed #9282: added a generic comment moderation toolkit. See the documentation for details.

This began life as (part of) James Bennett's comment-utils app, and was adapted to be part of Django by Thejaswi Puthraya and Jannis Leidel. Thanks, all!

git-svn-id: http://code.djangoproject.com/svn/django/trunk@10122 bcc190cf-cafb-0310-a4f2-bffc1f526a37