Add clone methods to Tile and Tile.Image, and add associated tests. r=crschmidt (closes #1296)

git-svn-id: http://svn.openlayers.org/trunk/openlayers@5854 dc9f47b5-9b13-0410-9fdd-eb0c1a62fdaf

lib/OpenLayers/Tile/Image.js

@@ -91,6 +91,34 @@ OpenLayers.Tile.Image = OpenLayers.Class(OpenLayers.Tile, {
         OpenLayers.Tile.prototype.destroy.apply(this, arguments);
     },
 
+    /**
+     * Method: clone
+     *
+     * Parameters:
+     * obj - {<OpenLayers.Tile.Image>} The tile to be cloned
+     *
+     * Returns:
+     * {<OpenLayers.Tile.Image>} An exact clone of this <OpenLayers.Tile.Image>
+     */
+    clone: function (obj) {
+        if (obj == null) {
+            obj = new OpenLayers.Tile.Image(this.layer, 
+                                            this.position, 
+                                            this.bounds, 
+                                            this.url, 
+                                            this.size);        
+        } 
+        
+        //pick up properties from superclass
+        obj = OpenLayers.Tile.prototype.clone.apply(this, [obj]);
+        
+        //dont want to directly copy the image div
+        obj.imgDiv = null;
+            
+        
+        return obj;
+    },
+    
     /**
      * Method: draw
      * Check that a tile should be drawn, and draw it.