documenting that Layer.VirtualEarth requires restrictedExtent to be set, and changing the examples accordingly. p=marcjansen (closes #3123)

git-svn-id: http://svn.openlayers.org/trunk/openlayers@11503 dc9f47b5-9b13-0410-9fdd-eb0c1a62fdaf

examples/bing.html

@@ -12,9 +12,18 @@
     <script>
 
         var map;
-
+ 
         function init(){
-            map = new OpenLayers.Map("map");
+            // setting restrictedExtent so that we can use the 
+            // VirtualEarth-layers, see e.g. 
+            // http://dev.openlayers.org/apidocs/files/OpenLayers/Layer/VirtualEarth-js.html
+            var restrictedExtent = new OpenLayers.Bounds(-20037508, -20037508, 
+                20037508, 20037508);
+            
+            map = new OpenLayers.Map("map", {
+                restrictedExtent: restrictedExtent
+            });
+            
             map.addControl(new OpenLayers.Control.LayerSwitcher());
 
             var shaded = new OpenLayers.Layer.VirtualEarth("Shaded", {