Enable testMultilinkOrdering check. Fix back_anydbm to pass. The testMultilinkOrdering was commented out with a "some day" comment. Well some day is today. Works on anydbm and sqlite. CI will tell me if I need to fix mysql and postgres.

try:
    # Python 3+.
    from xmlrpc import client, server
    server.SimpleXMLRPCDispatcher
except (ImportError, AttributeError):
    # Python 2.
    import xmlrpclib as client  # noqa: F401
    import SimpleXMLRPCServer as server