Fixing ArcGISCache layer

This is done by caching the tileOrigin at grid creation time.

lib/OpenLayers/Layer/ArcGISCache.js

@@ -358,6 +358,17 @@ OpenLayers.Layer.ArcGISCache = OpenLayers.Class(OpenLayers.Layer.XYZ, {
         return OpenLayers.Layer.XYZ.prototype.clone.apply(this, [obj]);
     },
 
+    /**
+     * Method: initGriddedTiles
+     * 
+     * Parameters:
+     * bounds - {<OpenLayers.Bounds>}
+     */
+    initGriddedTiles: function(bounds) {
+        delete this._tileOrigin;
+        OpenLayers.Layer.XYZ.prototype.initGriddedTiles.apply(this, arguments);
+    },
+    
     /**
      * Method: getMaxExtent
      * Get this layer's maximum extent.
@@ -379,8 +390,11 @@ OpenLayers.Layer.ArcGISCache = OpenLayers.Class(OpenLayers.Layer.XYZ, {
      * {<OpenLayers.LonLat>} The tile origin.
      */
     getTileOrigin: function() {
-        var extent = this.getMaxExtent();
+        if (!this._tileOrigin) {
-        return new OpenLayers.LonLat(extent.left, extent.bottom);
+            var extent = this.getMaxExtent();
+            this._tileOrigin = new OpenLayers.LonLat(extent.left, extent.bottom);
+        }
+        return this._tileOrigin;
     },
 
    /**