Release notes and additional in-line comment

As suggested by @bartvde.

lib/OpenLayers/TileManager.js

@@ -342,6 +342,8 @@ OpenLayers.TileManager = OpenLayers.Class({
                 img.style.visibility = 'hidden';
             }
             tile.setImage(img);
+            // LRU - move tile to the end of the array to mark it as the most
+            // recently used
             OpenLayers.Util.removeItem(this.tileCacheIndex, tile.url);
             this.tileCacheIndex.push(tile.url);
         }