Minor docs fix for e11ccc76.

six_ provides compatibility functions to work around this change:

:func:`~six.iterkeys`, :func:`~six.iteritems`, and :func:`~six.itervalues`.

Django's bundled version adds :func:`~django.utils.six.iterlists` for

It also contains an undocumented ``iterlists`` function that works well for

``django.utils.datastructures.MultiValueDict`` and its subclasses.

:class:`~django.http.HttpRequest` and :class:`~django.http.HttpResponse` objects