fix stone-to-flesh on petrified long worm

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.

src/zap.c

@@ -1,4 +1,4 @@
-/* NetHack 3.6	zap.c	$NHDT-Date: 1589491666 2020/05/14 21:27:46 $  $NHDT-Branch: NetHack-3.7 $:$NHDT-Revision: 1.340 $ */
+/* NetHack 3.6	zap.c	$NHDT-Date: 1591178401 2020/06/03 10:00:01 $  $NHDT-Branch: NetHack-3.7 $:$NHDT-Revision: 1.341 $ */
 /* Copyright (c) Stichting Mathematisch Centrum, Amsterdam, 1985. */
 /*-Copyright (c) Robert Patrick Rankin, 2013. */
 /* NetHack may be freely redistributed.  See license for details. */
@@ -586,6 +586,11 @@ boolean adjacentok; /* False: at obj's spot only, True: nearby is allowed */
             return (struct monst *) 0;
         mtmp = makemon(mtmp2->data, cc->x, cc->y,
                        (NO_MINVENT | MM_NOWAIT | MM_NOCOUNTBIRTH
+                        /* in case mtmp2 is a long worm; saved traits for
+                           long worm don't include tail segments so don't
+                           give mtmp any; it will be given a new 'wormno'
+                           though unless those are exhausted */
+                        | MM_NOTAIL
                         | (adjacentok ? MM_ADJACENTOK : 0)));
         if (!mtmp) {
             /* mtmp2 is a copy of obj's object->oextra->omonst extension