SetGroup Write command

[guyton%rand-unix at sri-unix.UUCP]

I plugged this hole here a little over a year ago by making the
ttys owned by a special group "write", and had the write command
be setgid to that group.  Seems to make more sense to me than yet
another setuid-root program floating around.

In case you want to do the same thing, the changes were:

  /etc/group: added "write" group with no logins. Only for write pgm!
  write.c:    closed other terminal before exec of shell
  write.c:    set group id back to real id before exec of shell
  write.c:    map outgoing control characters into ^X form
  write.c:    stat checks now for 020 bit instead of 002 bit
  login.c:    change of tty group to "write" group.  chmod to 620
  mesg.c:     change to use 020 bit instead of 022
  finger.c:   checks for stat 0220 instead of 0222 for "messages off" logic


-- Jim Guyton