better variable names for ext registry
better variable names for ext registry

cosmo0920/msgpack-ruby,ojundt/msgpack-ruby,ojundt/msgpack-ruby,cosmo0920/msgpack-ruby,msgpack/msgpack-ruby,ojundt/msgpack-ruby,cosmo0920/msgpack-ruby,ojundt/msgpack-ruby,cosmo0920/msgpack-ruby,msgpack/msgpack-ruby,msgpack/msgpack-ruby