non-static.
(channel_forward_start_read): New function.
(channel_forward_start_io): Use channel_forward_start_read.
(do_channel_forward_event): Use channel_forward_start_read.
Recognize CHANNEL_EVENT_DENY and CHANNEL_EVENT_CLOSE, and do
nothing.
(init_channel_forward): Take event handler as argument.
(make_channel_forward): Pass do_channel_forward_event to
init_channel_forward.
(forward_open_report, catch_channel_open): Deleted.

Rev: src/channel_forward.c:1.14.2.6