correctly identify getParameterString as a Util function

git-svn-id: http://svn.openlayers.org/trunk/openlayers@149 dc9f47b5-9b13-0410-9fdd-eb0c1a62fdaf

lib/OpenLayers/Layer/Grid.js

@@ -199,7 +199,7 @@ OpenLayers.Layer.Grid.prototype = Object.extend( new OpenLayers.Layer(), {
         
         // concat tile params with layer params and convert to string
         var allParams = Object.extend(params, this.params);
-        var paramsString = OpenLayers.getParameterString(allParams);
+        var paramsString = OpenLayers.Util.getParameterString(allParams);
 
         var server = this.url;
         var lastServerChar = server.charAt(server.length - 1);