don't fire changelayer events without a property, and do a more solid changelayer event check before changing the layer zIndex. r=tschaub (closes #3377)

git-svn-id: http://svn.openlayers.org/trunk/openlayers@12121 dc9f47b5-9b13-0410-9fdd-eb0c1a62fdaf

lib/OpenLayers/Layer/GoogleNG.js

@@ -205,7 +205,10 @@ OpenLayers.Layer.GoogleNG = OpenLayers.Class(OpenLayers.Layer.XYZ, {
             mapType: this.type,
             mapData: mapData
         });
-        this.map && this.map.events.triggerEvent("changelayer", {layer: this});
+        this.map && this.map.events.triggerEvent("changelayer", {
+            layer: this,
+            property: "attribution"
+        });
     },
     
     /**