patch for #452 - Adding events to Layer class to signal the start, end, and cancelling of a layer load. Thanks to Bart for the idea and followthrough with this patch.

git-svn-id: http://svn.openlayers.org/trunk/openlayers@2200 dc9f47b5-9b13-0410-9fdd-eb0c1a62fdaf

lib/OpenLayers/Layer.js

@@ -18,6 +18,15 @@ OpenLayers.Layer.prototype = {
     /** @type DOMElement */
     div: null,
 
+    /** supported application event types
+     * 
+     * @type Array */
+    EVENT_TYPES: [ 
+        "loadstart", "loadend", "loadcancel"],
+
+    /** @type OpenLayers.Events */
+    events: null,
+
     /** This variable is set when the layer is added to the map, via the 
      *  accessor function setMap()
      * 
@@ -121,6 +130,8 @@ OpenLayers.Layer.prototype = {
             this.div.style.height = "100%";
             this.div.id = this.id;
         }
+
+        this.events = new OpenLayers.Events(this, this.div, this.EVENT_TYPES);
     },
     
     /**
@@ -135,6 +146,7 @@ OpenLayers.Layer.prototype = {
         this.name = null;
         this.div = null;
         this.options = null;
+        this.events = null;
     },
     
    /**