create parent event target for the map, to allow stopping event propagation

src/ol/Map.js

@@ -108,6 +108,13 @@ ol.Map = function() {
      * @type {Element}
      */
     this.container_ = null;
+
+    // Create an EventTarget and set it as the map's parent EventTarget. With
+    // this we can have two groups of listeners: "map listeners" and "map
+    // parent listeners". And map listeners can stop event propagation, and
+    // thereby prevent map parent listeners from receiving events.
+    this.setParentEventTarget(new goog.events.EventTarget());
+
 };
 goog.inherits(ol.Map, goog.events.EventTarget);