Merge pull request #4429 from fredj/object_change_evt

Dispatch a change event only if the value changes

src/ol/object.js

@@ -206,7 +206,9 @@ ol.Object.prototype.set = function(key, value, opt_silent) {
   } else {
     var oldValue = this.values_[key];
     this.values_[key] = value;
-    this.notify(key, oldValue);
+    if (oldValue !== value) {
+      this.notify(key, oldValue);
+    }
   }
 };