petrified engulfer (display glitch & potential panic)

petrified engulfer (display glitch & potential panic)

     From the newsgroup:  if you were polymorped into a cockatrice and
a trapper attempted to swallow you, the 't' displayed at its location
would be left behind after it turned to stoned.  This fixes that and a
much more serious issue as well:  if you were punished at the time, the
game would panic on your next attempt to move because the ball&chain were
left in limbo.  There would also have been strangeness (monster sharing
your location, stale u.ustuck setting) if the swallower was life-saved,
but I didn't try to make that happen so am not sure how bad things would
have been.