Method for getting both feature id and data.

Having to call two methods to get complete feature information (id and data) is cumbersome.  The `getFeatureInfo` method returns an object with both feature id and data.

lib/OpenLayers/Tile/UTFGrid.js

@@ -146,22 +146,29 @@ OpenLayers.Tile.UTFGrid = OpenLayers.Class(OpenLayers.Tile, {
     },
     
     /**
-     * Method: getFeatureData
-     * Get feature data associated with a pixel offset.
+     * Method: getFeatureInfo
+     * Get feature information associated with a pixel offset.  If the pixel
+     *     offset corresponds to a feature, the returned object will have id
+     *     and data properties.  Otherwise, null will be returned.
+     *     
      *
      * Parameters:
      * i - {Number} X-axis pixel offset (from top left of tile)
      * j - {Number} Y-axis pixel offset (from top left of tile)
      *
      * Returns:
-     * {Object} The UTFGrid data corresponding to the given pixel offset.
+     * {Object} Object with feature id and data properties corresponding to the 
+     *     given pixel offset.
      */
-    getFeatureData: function(i, j) {
-        var data;
+    getFeatureInfo: function(i, j) {
+        var info = null;
         if (this.json) {
-            data = this.json.data[this.getFeatureId(i, j)];
+            var id = this.getFeatureId(i, j);
+            if (id !== null) {
+                info = {id: id, data: this.json.data[id]};
+            }
         }
-        return data;
+        return info;
     },
     
     /**
@@ -174,16 +181,20 @@ OpenLayers.Tile.UTFGrid = OpenLayers.Class(OpenLayers.Tile, {
      *
      * Returns:
      * {Object} The feature identifier corresponding to the given pixel offset.
+     *     Returns null if pixel doesn't correspond to a feature.
      */
     getFeatureId: function(i, j) {
-        var id;
+        var id = null;
         if (this.json) {
             var resolution = this.utfgridResolution;
             var row = Math.floor(j / resolution);
             var col = Math.floor(i / resolution);
             var charCode = this.json.grid[row].charCodeAt(col);
             var index = this.indexFromCharCode(charCode);
-            id = this.json.keys[index];
+            var keys = this.json.keys;
+            if (!isNaN(index) && (index in keys)) {
+                id = keys[index];
+            }
         }
         return id;
     },