Convert the vibrating square to a trap

Patch due to ais523 in NetHack 4.

This is not ready to be merged yet; the vibrating square needs a tile
image for tiles builds.

src/sp_lev.c

@@ -735,6 +735,7 @@ rndtrap()
         rtrap = rnd(TRAPNUM - 1);
         switch (rtrap) {
         case HOLE: /* no random holes on special levels */
+        case VIBRATING_SQUARE:
         case MAGIC_PORTAL:
             rtrap = NO_TRAP;
             break;