change diff to add in OpenLayers.LonLat. Even though it is not used, it is probably better to have all these Util objects be consistent. See [129]

git-svn-id: http://svn.openlayers.org/trunk/openlayers@131 dc9f47b5-9b13-0410-9fdd-eb0c1a62fdaf

lib/OpenLayers/Util.js

@@ -175,13 +175,15 @@ OpenLayers.LonLat.prototype = {
     },
 
     /** 
-    * @param {OpenLayers.LonLat} ll
+    * @param {float} lon
+    * @param {float} lat
     *
-    * @return OpenLayers.LonLat object with difference between the two coords
+    * @return A new OpenLayers.LonLat object with the lon and lat passed-in
+    *         added to this's. 
     * @type OpenLayers.Pixel
     */
-    diff:function(ll) {
-        return new OpenLayers.LonLat(this.lon - ll.lon, this.lat - ll.lat);
+    add:function(lon, lat) {
+        return new OpenLayers.LonLat(this.lon + lon, this.lat + lat);
     },
 
     /**