Fixed #5756, #6296 -- Most template tags can now handle filters in arguments.

Most of the hard work for this was done by akaihola.

There are still possibly some problems with the i18n template tags,
since they are written quite differently and a few other bug fixes have
to made before they can be fixed.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@10119 bcc190cf-cafb-0310-a4f2-bffc1f526a37