Fix error in ModelState.clone() not copying deep enough

    Represents a Django Model. We don't use the actual Model class

    as it's not designed to have its options changed - instead, we

    mutate this one and then render it into a Model as required.

    Note that while you are allowed to mutate .fields, you are not allowed

    to mutate the Field instances inside there themselves - you must instead

    assign new ones, as these are not detached during a clone.

    """

    def __init__(self, app_label, name, fields, options=None, bases=None):

        return self.__class__(

            app_label = self.app_label,

            name = self.name,

            fields = self.fields,

            options = self.options,

            fields = list(self.fields),

            options = dict(self.options),

            bases = self.bases,

        )