fix #332 - strangulation affects headless monsters (trunk only)

From a bug report:  amulet of strangulation
continues to kill hero if he polymorphs into a creature which doesn't
need to breathe or doesn't have a head or even a circulatory system.
Currently, the messages are different when the hero doesn't need to
breathe, but that doesn't seem good enough.  This makes strangulation
stop when you polymorph into something which shouldn't be vulnerable and
restart if you poly into something vulnerable while still wearing the
bad amulet.

     can_be_strangled() is doing more checks that necessary, in case the
strangulation property ever gets conferred by something other than an
amulet.  Its criteria for protection from strangling might need tweaking.

src/do_wear.c

@@ -1,4 +1,4 @@
-/*	SCCS Id: @(#)do_wear.c	3.5	2007/03/19	*/
+/*	SCCS Id: @(#)do_wear.c	3.5	2007/05/16	*/
 /* Copyright (c) Stichting Mathematisch Centrum, Amsterdam, 1985. */
 /* NetHack may be freely redistributed.  See license for details. */
 
@@ -626,9 +626,11 @@ Amulet_on()
 		break;
 	    }
 	case AMULET_OF_STRANGULATION:
-		makeknown(AMULET_OF_STRANGULATION);
-		pline("It constricts your throat!");
-		Strangled = 6;
+		if (can_be_strangled(&youmonst)) {
+		    makeknown(AMULET_OF_STRANGULATION);
+		    pline("It constricts your throat!");
+		    Strangled = 6L;
+		}
 		break;
 	case AMULET_OF_RESTFUL_SLEEP:
 		HSleeping = rnd(100);
@@ -671,8 +673,11 @@ Amulet_off()
 		break;
 	case AMULET_OF_STRANGULATION:
 		if (Strangled) {
+		    if (Breathless)
+			Your("%s is no longer constricted!", body_part(NECK));
+		    else
 			You("can breathe more easily!");
-			Strangled = 0;
+		    Strangled = 0L;
 		}
 		break;
 	case AMULET_OF_RESTFUL_SLEEP: