Layer and tile API update.

The tile now has responsibility for resolving feature ids and fetching feature data given x, y pixel offsets with getFeatureId and getFeatureData methods.  The layer has corresponding getFeatureId and getFeatureData methods that take a map location, lookup the appropriate tile, and delegate to the tile for the rest of the work.

lib/OpenLayers/Control/UTFGrid.js

@@ -180,7 +180,7 @@ OpenLayers.Control.UTFGrid = OpenLayers.Class(OpenLayers.Control, {
             for (var i=0, len=layers.length; i<len; i++) {
                 layer = layers[i];
                 idx = this.map.layers.indexOf(layer);
-                dataLookup[idx] = layer.getData(lonLat);
+                dataLookup[idx] = layer.getFeatureData(lonLat);
             }
             this.callback(dataLookup); // perhaps pass tile, lonLat?
         }