add hook to trigger the drawing of a layer upon addition to the map (assuming a center has been set)

git-svn-id: http://svn.openlayers.org/trunk/openlayers@895 dc9f47b5-9b13-0410-9fdd-eb0c1a62fdaf

lib/OpenLayers/Map.js

@@ -250,6 +250,12 @@ OpenLayers.Map.prototype = {
 
         this.events.triggerEvent("addlayer");
 
+        //make sure layer draws itself!
+        if (this.center != null) {
+            var bounds = this.getExtent();
+            layer.moveTo(bounds, true);
+        }
+
         // hack hack hack - until we add a more robust layer switcher,
         //   which is able to determine which layers are base layers and 
         //   which are not (and put baselayers in a radiobutton group and