Unroll choices iterators in field deconstruction

        equals_comparison = set(["choices", "validators", "db_tablespace"])

        for name, default in possibles.items():

            value = getattr(self, attr_overrides.get(name, name))

            # Unroll anything iterable for choices into a concrete list

            if name == "choices" and isinstance(value, collections.Iterable):

                value = list(value)

            # Do correct kind of comparison

            if name in equals_comparison:

                if value != default:

                    keywords[name] = value