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

- Fix assertion that key size is exactly curve size

--HG--
rename : random.c => dbrandom.c
rename : random.h => dbrandom.h