(class gateway_channel): New class.
(do_kill_gateway_channel): New function.
(do_receive): Use channel_transmit_data and
channel_transmit_extended, on the chained channel.
(do_send_adjust): Use channel_adjust_rec_window.
(do_gateway_channel_event): New function.
(do_gateway_channel_request): New function.
(do_gateway_channel_success): New function.
(do_gateway_channel_failure): New function.
(gateway_request_methods): New method struct.
(make_gateway_pair): New function.
(gateway_handle_channel_open): New function.
(gateway_packet_handler): New function.

Rev: src/gateway_channel.c:1.18.2.3