docs: def is_backup_class(cls):
      """Return true if given class supports back up. Currently this means a
      gludb.data.Storable-derived class that has a mapping as defined in
      gludb.config"""
      return True if (
          isclass(cls) and
          issubclass(cls, Storable) and
          get_mapping(cls, no_mapping_ok=True)
      ) else False