[1.2.X] Removed compatibility with Sphinx < 1.0 workarounds in our extension...

[1.2.X] Removed compatibility with Sphinx < 1.0 workarounds in our extension code. Also, started to use the 'needs_sphinx' Sphinx config var.

Follow up on r14624.

Backport of [14631] from trunk

git-svn-id: http://code.djangoproject.com/svn/django/branches/releases/1.2.X@14633 bcc190cf-cafb-0310-a4f2-bffc1f526a37