(make_global_request_exception_handler, handle_global_request)
(do_exc_channel_request_handler)
(make_channel_request_exception_handler, handle_channel_request)
(do_exc_channel_open_handler, make_exc_channel_open_handler)
(handle_channel_open, handle_channel_failure): Adapted to new
simpler exception abstraction.

Rev: src/channel.c:1.125.2.13