`ModelAdmin` validation now runs when using the `site.register(Model, **kwargs)` form.

        If a model is already registered, this will raise AlreadyRegistered.

        """

        if not admin_class:

            admin_class = ModelAdmin

        # Don't import the humongous validation code unless required

        if admin_class and settings.DEBUG:

            from django.contrib.admin.validation import validate

        else:

            validate = lambda model, adminclass: None

        if not admin_class:

            admin_class = ModelAdmin

        if isinstance(model_or_iterable, ModelBase):

            model_or_iterable = [model_or_iterable]

        for model in model_or_iterable: