Merge pull request #2133 from fredj/ol.ObjectEvent.key

Export ol.ObjectEvent#key property

src/ol/object.js

@@ -50,6 +50,7 @@ ol.ObjectEvent = function(type, key) {
   /**
    * The name of the property whose value is changing.
    * @type {string}
+   * @todo api
    */
   this.key = key;