magic whistle vs steed

From a bug report, using a magic whistle when
you're mounted and standing on a trap location would cause your steed to
trigger the trap even though it didn't move.  Since it is already at the
same place as you, make steed be unaffected by magic whistle so that trap
complications can be avoided.

src/apply.c

@@ -441,6 +441,11 @@ struct obj *obj;
 		for(mtmp = fmon; mtmp; mtmp = nextmon) {
 		    nextmon = mtmp->nmon; /* trap might kill mon */
 		    if (DEADMONSTER(mtmp)) continue;
+#ifdef STEED
+		    /* steed is already at your location, so not affected;
+		       this avoids trap issues if you're on a trap location */
+		    if (mtmp == u.usteed) continue;
+#endif
 		    if (mtmp->mtame) {
 			if (mtmp->mtrapped) {
 			    /* no longer in previous trap (affects mintrap) */