give Grid a clone() function.

git-svn-id: http://svn.openlayers.org/trunk/openlayers@894 dc9f47b5-9b13-0410-9fdd-eb0c1a62fdaf

lib/OpenLayers/Layer/Grid.js

@@ -47,6 +47,27 @@ OpenLayers.Layer.Grid.prototype =
         OpenLayers.Layer.HTTPRequest.prototype.destroy.apply(this, arguments); 
     },
 
+    /**
+     * @param {Object} obj
+     * 
+     * @returns An exact clone of this OpenLayers.Layer.Grid
+     * @type OpenLayers.Layer.Grid
+     */
+    clone: function (obj) {
+        
+        if (obj == null) {
+            obj = new OpenLayers.Layer.Grid(this.name,
+                                            this.url,
+                                            this.params,
+                                            this.options);
+        }
+        
+        //set any non-init vars here
+        
+        //get all additions from superclasses
+        return OpenLayers.Layer.HTTPRequest.prototype.clone.apply(this, [obj]);
+    },    
+
     /** When the layer is added to a map, then we can ask the map for
      *   its default tile size
      *