be more precise about maximum channel sizes

- Fix port forwards with a bind address of 127.0.0.1 vs "localhost" etc

we're waiting for a key exchange.

This should hopefully fix the situation where "~." doesn't work to terminate a
client session when a laptop wakes up. The client will be stuck waiting for a
key exchange on a dead connection, so won't have read the escape character

- Use _exit() in segv handler

have a manpage

  time
- Set non-pty connections to bulk for client and server