Fixed #16927 -- Corrected the `{% ifchanged %}` template tag's documentation....

Fixed #16927 -- Corrected the `{% ifchanged %}` template tag's documentation. Thanks to sebastian for the report and patch.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@16902 bcc190cf-cafb-0310-a4f2-bffc1f526a37