Added versionadded annotations for redirect middleware attributes.

    .. attribute:: response_gone_class

        ..  versionadded:: 1.7

        The :class:`~django.http.HttpResponse` class used when a

        :class:`~django.contrib.redirects.models.Redirect` is not

        found for the requested path or has a blank ``new_path``

    .. attribute:: response_redirect_class

        ..  versionadded:: 1.7

        The :class:`~django.http.HttpResponse` class that handles the

        redirect.