SelectFeature control can now select across multiple vector

layers when passed an array of layers instead of a single layer with 
the constructor. This changeset also introduces a new layer type, 
Layer.Vector.RootContainer, which will be set as the topmost layer by 
the SelectFeature control and collect the svg/vml/canvas roots of 
multiple vector layers. r=crschmidt (closes #1666)


git-svn-id: http://svn.openlayers.org/trunk/openlayers@9116 dc9f47b5-9b13-0410-9fdd-eb0c1a62fdaf

lib/OpenLayers/Renderer/VML.js

@@ -810,6 +810,26 @@ OpenLayers.Renderer.VML = OpenLayers.Class(OpenLayers.Renderer.Elements, {
         return node;
     },
     
+    /**
+     * Method: moveRoot
+     * moves this renderer's root to a different renderer.
+     * 
+     * Parameters:
+     * renderer - {<OpenLayers.Renderer>} target renderer for the moved root
+     * root - {DOMElement} optional root node. To be used when this renderer
+     *     holds roots from multiple layers to tell this method which one to
+     *     detach
+     * 
+     * Returns:
+     * {Boolean} true if successful, false otherwise
+     */
+    moveRoot: function(renderer) {
+        var layer = this.map.getLayer(this.container.id);
+        layer && this.clear();
+        OpenLayers.Renderer.Elements.prototype.moveRoot.apply(this, arguments);
+        layer && layer.redraw();
+    },
+    
     /**
      * Method: importSymbol
      * add a new symbol definition from the rendererer's symbol hash