change macro for control characters, use system predefined values as much as

change macro for control characters, use system predefined values as much as
possible, fix usage message for settable interrupt, merge in reset code from
/usr/ucb/reset (from when different), change defaults to agree with kernel
defaults, always set window size if not previously set, use initialization
information from termcap if reset info doesn't exist (rs->is, rf->if)
(Major portion of work done by Serge)

SCCS-vsn: usr.bin/tset/tset.c 5.6