'add a config as one of the global configs.
If there are no configs set up yet, this config also
gets set as the "_current".'

@classmethod
def register(cls, db, db_opts, options, file_config, namespace):

    cfg = Config(db, db_opts, options, file_config)
    global _current
    if (not _current):
        cls.set_as_current(cfg, namespace)
    cls._configs[cfg.db.name] = cfg
    cls._configs[(cfg.db.name, cfg.db.dialect)] = cfg
    cls._configs[cfg.db] = cfg
