buglist: cutting Shopkeeper the long worm

Cutting a shopkeeper poly'd as a long worm would generate strange messages
and could result in a crash.  cutworm didn't deal with all the intricacies
of duplicating a monster.   Fixed by changing cutworm() to use clone_mon()
to do most of its dirty work.  It seems to me that without this change,
cutting a tame long worm could also have similar bad effects.
Other side effects of this change:
- clone_mon now takes x,y coordinates, 0,0 results in previous behavior
- clone_mon no longer always makes cloned monsters tame/peaceful if player
  caused the clone, using the same formula previously in cutworm.  Someone
  else may wish to tweak this for gremlins.
- clone_mon will christen the new mon with the old shopkeeper's name, even
  though clones are never shopkeepers (game can't handle 2 for a shop)
- cutworm can now be called during conflict or pet combat, although I
  added no such calls (yet)

src/mhitm.c

@@ -280,7 +280,7 @@ mattackm(magr, mdef)
 		       && otmp && objects[otmp->otyp].oc_material == IRON
 		       && mdef->mhp > 1 && !mdef->mcan)
 		    {
-			if (clone_mon(mdef)) {
+			if (clone_mon(mdef, 0, 0)) {
 			    if (vis) {
 				char buf[BUFSZ];