code: function(evt) {
          var tile = evt.object;
          tile.events.un({
              beforedraw: this.queueTileDraw,
              beforeload: this.manageTileCache,
              loadend: this.addToCache,
              unload: this.unloadTile,
              scope: this
          });
          OpenLayers.Util.removeItem(this.tileQueue[tile.layer.map.id], tile);
      }
docs: Method: unloadTile
  Listener for the tile's unload event
  
  Parameters:
  evt - {Object} The listener argument