Use event handling of OpenLayers.Event, not the native one.

Also includes some of the fixes suggested by @bartvde.

lib/OpenLayers/Events/buttonclick.js

@@ -77,39 +77,20 @@ OpenLayers.Events.buttonclick = OpenLayers.Class({
         }
         OpenLayers.Util.extend(this, options);
         
-        this._buttonClick = OpenLayers.Function.bindAsEventListener(
-            this.buttonClick, this
-        );
-        this.observe();
-    },
-    
-    /**
-     * Method: observe
-     */
-    observe: function() {
         for (var i=this.events.length-1; i>=0; --i) {
-            OpenLayers.Event.observe(
-                this.target.element, this.events[i], this._buttonClick
-            );            
-        };
-    },
-    
-    /**
-     * Method: stopObserving
-     */
-    stopObserving: function() {
-        for (var i=this.events.length-1; i>=0; --i) {
-            OpenLayers.Event.stopObserving(
-                this.target.element, this.events[i], this._buttonClick
-            );            
+            this.target.register(this.events[i], this, this.buttonClick, {
+                extension: true
+            });
         }
     },
-
+    
     /**
      * Method: destroy
      */
     destroy: function() {
-        this.stopObserving()
+        for (var i=this.events.length-1; i>=0; --i) {
+            this.target.unregister(this.events[i], this, this.buttonClick);
+        }
     },
 
     /**
@@ -120,8 +101,9 @@ OpenLayers.Events.buttonclick = OpenLayers.Class({
      * evt - {Event}
      */
     buttonClick: function(evt) {
-        if (OpenLayers.Event.isLeftClick(evt) || !~evt.type.indexOf("mouse")) {
-            var element = OpenLayers.Event.element(evt);
+        var propagate = true,
+            element = OpenLayers.Event.element(evt);
+        if (element && (OpenLayers.Event.isLeftClick(evt) || !~evt.type.indexOf("mouse"))) {
             if (OpenLayers.Element.hasClass(element, "olAlphaImg")) {
                 element = element.parentNode;
             }
@@ -135,16 +117,19 @@ OpenLayers.Events.buttonclick = OpenLayers.Class({
                     if (this.cancelRegEx.test(evt.type)) {
                         delete this._buttonStarted;
                     }
-                    OpenLayers.Event.stop(evt, false, true);
+                    OpenLayers.Event.stop(evt, false);
+                    propagate = false;
                 }
                 if (this.startRegEx.test(evt.type)) {
                     this._buttonStarted = true;
-                    OpenLayers.Event.stop(evt, false, true);
+                    OpenLayers.Event.stop(evt, false);
+                    propagate = false;
                 }
             } else {
                 delete this._buttonStarted;
             }
         }
+        return propagate;
     }
     
 });