'Validate that list_display_links is a unique subset of list_display.'

def validate_list_display_links(self, cls, model):

    if hasattr(cls, 'list_display_links'):
        check_isseq(cls, 'list_display_links', cls.list_display_links)
        for (idx, field) in enumerate(cls.list_display_links):
            if (field not in cls.list_display):
                raise ImproperlyConfigured(("'%s.list_display_links[%d]'    refers    to    '%s'    which    is    not    defined    in    'list_display'." % (cls.__name__, idx, field)))
