cancellation, polymorphed and unchanging

<Someone> reported that a wand of cancellation would ignore Unchanging,
noting the case of cancelling yourself while polymorphed into a stone golem.
He thought the wand should win, killing the player.  I felt otherwise,
since the case he specified passes the flag allow_cancel_kill == FALSE.

doc/fixes34.1

@@ -148,6 +148,7 @@ knights should be able to avenge attacks from covetous monsters
 eating various rotten food items would not break vegan/vegetarian conduct
 unaligned special levels should inherit alignment from the dungeon
 Samurai quest was missing several doors
+Cancelled while polymorphed and Unchanging should provide feedback
 
 
 Platform- and/or Interface-Specific Fixes

src/eat.c

@@ -1496,7 +1496,8 @@ struct obj *otmp;
 	    case AMULET_OF_RESTFUL_SLEEP: /* another bad idea! */
 		HSleeping = FROMOUTSIDE | rnd(100);
 		break;
-		case RIN_SUSTAIN_ABILITY:
+	    case RIN_SUSTAIN_ABILITY:
+	    case AMULET_OF_UNCHANGING:
 	    case AMULET_OF_LIFE_SAVING:
 	    case AMULET_OF_REFLECTION: /* nice try */
 	    /* can't eat Amulet of Yendor or fakes,

src/zap.c

@@ -2213,7 +2213,11 @@ boolean			youattack, allow_cancel_kill, self_cancel;
 	    if (Upolyd) {
 		if ((u.umonnum == PM_CLAY_GOLEM) && !Blind)
 		    pline(writing_vanishes, your);
-		rehumanize();
+
+		if (Unchanging)
+		    Your("amulet grows hot for a moment, then cools.");
+		else
+		    rehumanize();
 	    }
 	} else {
 	    mdef->mcan = TRUE;