[1.1.X] Corrected a markup error in middleware docs. Backport of applicable...

[1.1.X] Corrected a markup error in middleware docs. Backport of applicable bits of [12759] from trunk.

git-svn-id: http://code.djangoproject.com/svn/django/branches/releases/1.1.X@12760 bcc190cf-cafb-0310-a4f2-bffc1f526a37