[authfd.c authfile.c channels.c kexdh.c kexgex.c packet.c ssh.c sshconnect.c sshconnect1.c] use xxx_put_cstring()
[kex.c kex.h kexdh.c kexgex.c packet.c sshconnect2.c sshd.c] don't sent multiple kexinit-requests. send newkeys, block while waiting for newkeys. fix comments.