(do_handle_kexinit): Check length of received kex_algorithms list.
(do_handle_kexinit): Set kex_state to KEX_STATE_IGNORE or
KEX_STATE_IN_PROGRESS as appropriate.
(do_handle_newkeys): Clear kexinits and literal_kexinits when
resetting kex_state (fixes key renegotiation bug reported by jps).
(kexinit_filter): New command.

Rev: src/keyexchange.c:1.71
Rev: src/keyexchange.h:1.47