Add some buffer overrun fixes from OpenBSD and myself.
Add skey calculator kludge from OpenBSD.
TODO: do a real merge of dab's sources... probably just make telnet and
telnetd contrib software.
Obtained from: OpenBSD, dab@bsdi.com
Telnet has nothing to do with this, it's telnetd and telnetd
doesn't use KLUDGELINEMODE so that theory is washed up. Anyway,
back out previous commit and slink away with red face.