New tile image cache and tile queue improvements

We now reuse tile images by maintaining a cache of image elements with a
simplified LRU expiry policy (by order, not by timestamp). The tile queue
is bypassed for images that are available in the cache, so they can be
rendered immediately. And the tile queue itself loads more than just one
image at a time now (2 per layer url).

lib/OpenLayers/Layer/Bing.js

@@ -201,13 +201,13 @@ OpenLayers.Layer.Bing = OpenLayers.Class(OpenLayers.Layer.XYZ, {
     },
 
     /**
-     * Method: drawTileFromQueue
-     * Draws the first tile from the tileQueue, and unqueues that tile
+     * Method: drawTilesFromQueue
+     * Draws tiles from the tileQueue, and unqueues the tiles
      */
-    drawTileFromQueue: function() {
+    drawTilesFromQueue: function() {
         // don't start working on the queue before we have a url from initLayer
         if (this.url) {
-            OpenLayers.Layer.XYZ.prototype.drawTileFromQueue.apply(this, arguments);
+            OpenLayers.Layer.XYZ.prototype.drawTilesFromQueue.apply(this, arguments);
         }
     },