Fix bz276,H4172: Fleeing monsters don't actually flee

This fix comes via DynaHack by Tung Nguyen.

src/monmove.c

@@ -271,6 +271,8 @@ boolean fleemsg;
         }
         mtmp->mflee = 1;
     }
+    /* ignore recently-stepped spaces when made to flee */
+    memset(mtmp->mtrack, MTSZ, sizeof(coord));
 }
 
 STATIC_OVL void