Activating strategies after adding the layer to the map. r=elemoine (closes #1920)

git-svn-id: http://svn.openlayers.org/trunk/openlayers@9266 dc9f47b5-9b13-0410-9fdd-eb0c1a62fdaf

lib/OpenLayers/Layer.js

@@ -529,6 +529,14 @@ OpenLayers.Layer = OpenLayers.Class({
         }
     },
     
+    /**
+     * Method: afterAdd
+     * Called at the end of the map.addLayer sequence.  At this point, the map
+     *     will have a base layer.  To be overridden by subclasses.
+     */
+    afterAdd: function() {
+    },
+    
     /**
      * APIMethod: removeMap
      * Just as setMap() allows each layer the possibility to take a