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.

util/lev_main.c

@@ -173,6 +173,7 @@ static struct {
                    { "magic", MAGIC_TRAP },
                    { "anti magic", ANTI_MAGIC },
                    { "polymorph", POLY_TRAP },
+                   { "vibrating square", VIBRATING_SQUARE },
                    { 0, 0 } };
 
 static struct {