Don't queue tiles multiple times.

This results in a smaller queue that we don't have to unqueue from.

lib/OpenLayers/Layer/Grid.js

@@ -414,7 +414,11 @@ OpenLayers.Layer.Grid = OpenLayers.Class(OpenLayers.Layer.HTTPRequest, {
      * evt - {Object} Listener argument of the tile's beforedraw event
      */
     queueTileDraw: function(evt) {
-        this.tileQueue.push(evt.object);
+        var tile = evt.object;
+        if (!~OpenLayers.Util.indexOf(this.tileQueue, tile)) {
+            // queue only if not in queue already
+            this.tileQueue.push(tile);
+        }
         if (!this.tileQueueId) {
             this.tileQueueId = OpenLayers.Animation.start(
                 OpenLayers.Function.bind(this.drawTileFromQueue, this),
@@ -433,26 +437,10 @@ OpenLayers.Layer.Grid = OpenLayers.Class(OpenLayers.Layer.HTTPRequest, {
             this.clearTileQueue();
         } else {
             var tile = this.tileQueue.shift();
-            this.unqueueTile(tile);
             tile.draw(true);
         }
     },
     
-    /**
-     * Method: unqueueTile
-     * Removes all occurrences of a tile from the <tileQueue>.
-     *
-     * Parameters:
-     * tile - {<OpenLayers.Tile>} The tile to remove from the queue
-     */
-    unqueueTile: function(tile) {
-        for (var i=this.tileQueue.length-1; i>=0; --i) {
-            if (this.tileQueue[i] === tile) {
-                this.tileQueue.splice(i, 1);
-            }
-        }
-    },
-    
     /**
      * Method: clearTileQueue
      * Clears the animation queue
@@ -470,7 +458,6 @@ OpenLayers.Layer.Grid = OpenLayers.Class(OpenLayers.Layer.HTTPRequest, {
      * tile - {<OpenLayers.Tile>}
      */
     destroyTile: function(tile) {
-        this.unqueueTile(tile);
         this.removeTileMonitoringHooks(tile);
         tile.destroy();
     },