A rewrite of the reverse URL parsing: the reverse() call and the "url" template tag.

      This is fully backwards compatible, but it fixes a bunch of little bugs. Thanks
to SmileyChris and Ilya Semenov for some early patches in this area that were
incorporated into this change.

Fixed #2977, #4915, #6934, #7206.


git-svn-id: http://code.djangoproject.com/svn/django/trunk@8760 bcc190cf-cafb-0310-a4f2-bffc1f526a37