Added comment to UserAdmin.add_view() explaining why we disallow users without...

        return super(UserAdmin, self).__call__(request, url)

    def add_view(self, request):

        # It's an error for a user to have add permission but NOT change

        # permission for users. If we allowed such users to add users, they

        # could create superusers, which would mean they would essentially have

        # the permission to change users. To avoid the problem entirely, we

        # disallow users from adding users if they don't have change

        # permission.

        if not self.has_change_permission(request):

            raise PermissionDenied

        if request.method == 'POST':