make sure clone() of a layer does not copy the reference in the 'map' property. that should always be null as a cloned layer will still need to be added to the map via map.addLayer()

git-svn-id: http://svn.openlayers.org/trunk/openlayers@887 dc9f47b5-9b13-0410-9fdd-eb0c1a62fdaf

lib/OpenLayers/Layer.js

@@ -92,6 +92,10 @@ OpenLayers.Layer.prototype = {
         // catch any randomly tagged-on properties
         obj = OpenLayers.Util.applyDefaults(obj, this);
         
+        // a cloned layer should never have its map property set
+        //  because it has not been added to a map yet. 
+        obj.map = null;
+        
         return obj;
     },