montraits() didn't have any handling for long worm tails, makemon()
didn't have any provision for creating a long worm without a tail,
replmon() uses place_wegs() to put tail segments on the map when
replacing a dummy new monster with the mtraits one but place_wsegs()
wasn't updating the head segment since it isn't put on the map.
That turned out to be key because there is always an extra segment
co-located with the monster and when its coordinates were wrong,
worm_known() gave bad results for visibility checking. The
statue-goes-away message was the one for not being able to see the
monster that it just animated into, even though 'w' appeared at the
spot. It took quite a while to track down what was going on there.
Sanity checking for worms has been updated and could conceivably
start triggering complaints about things that it used ignore.
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