More robust array type check. p=mwootendev, r=me (closes #2959)

git-svn-id: http://svn.openlayers.org/trunk/openlayers@12095 dc9f47b5-9b13-0410-9fdd-eb0c1a62fdaf

lib/OpenLayers/Layer/XYZ.js

@@ -120,7 +120,7 @@ OpenLayers.Layer.XYZ = OpenLayers.Class(OpenLayers.Layer.Grid, {
     getURL: function (bounds) {
         var xyz = this.getXYZ(bounds);
         var url = this.url;
-        if (url instanceof Array) {
+        if (OpenLayers.Util.isArray(url)) {
             var s = '' + xyz.x + xyz.y + xyz.z;
             url = this.selectUrl(s, url);
         }