Disable key-expire timer during the key exchange.
(make_kexinit_handler): Deleted init argument, it's now stored
with the connection.
(SESSION_KEY_LIFETIME_CLIENT, SESSION_KEY_LIFETIME_SERVER): New
constants.
(do_handle_newkeys): Install key expire timeout.
(set_reexchange_timeout): New function.

Rev: src/keyexchange.c:1.83
Rev: src/keyexchange.h:1.55