Merge pull request #874 from ahocevar/tilemanager-backbuffer-id

Tile images should not have an id. r=@bartvde

lib/OpenLayers/TileManager.js

@@ -363,6 +363,8 @@ OpenLayers.TileManager = OpenLayers.Class({
                 img.style.opacity = 0;
                 img.style.visibility = 'hidden';
             }
+            // Only backbuffer tiles have an id, so we don't want one here
+            img.id = null;
             tile.setImage(img);
             // LRU - move tile to the end of the array to mark it as the most
             // recently used