eating mimic corpses

Don't mimic gold if you are Unchanging at the time you eat a
mimic corpse.

doc/fixes34.1

@@ -284,6 +284,7 @@ detect attempt to swap places with big pet through narrow opening
 stinking clouds in bones files do not get their ttl set reasonably
 stinking clouds in bones files may incorrectly set player_inside
 breaking wand of digging on a drawbridge shouldn't dig/hole a pit in the bridge
+avoid mimicking gold when the character has the Unchanging attribute
 
 
 Platform- and/or Interface-Specific Fixes

src/eat.c

@@ -834,7 +834,7 @@ register int pm;
 		/* fall into next case */
 	    case PM_SMALL_MIMIC:
 		tmp += 20;
-		if (youmonst.data->mlet != S_MIMIC) {
+		if (youmonst.data->mlet != S_MIMIC && !Unchanging) {
 		    char buf[BUFSZ];
 		    You_cant("resist the temptation to mimic a pile of gold.");
 #ifdef STEED