connection_send_kex_start. Use C_WRITE_NOW.
(do_handle_kexinit): Likewise.
(do_handle_newkeys): For uniformity, reset the NEWKEYS handler to
&connection_fail_handler, even though NULL should work fine.
(keyexchange_finish): Use C_WRITE_NOW. Call
connection_send_kex_end. #if:ed out the code sending DEBUG
messages at this point.

Rev: src/keyexchange.c:1.81
Rev: src/keyexchange.h:1.53