support for rightclick via dom contextmenu

[GoogleCodeExporter]

For this:
 * @name MarkerClustererPlus for Google Maps V3
 * @version 2.1.2 [May 28, 2014]
 * @author Gary Little

What feature would you like to see added?
DOM event "contextmenu" added to trigger/capture map cluster "rightclick" 
event. See below code:

At about line 183, with other events use: 
    google.maps.event.addDomListener(this.div_, "contextmenu", function () {
    var mc = cClusterIcon.cluster_.getMarkerClusterer();
    /**
     * This event is fired when the mouse right click a cluster marker.
     * @name MarkerClusterer#rightclick
     * @param {Cluster} c The cluster that the mouse right clicked.
     * @event
     */
    google.maps.event.trigger(mc, "rightclick", cClusterIcon.cluster_);
  });

Additional comments:

Original issue reported on code.google.com by powerspa...@gmail.com on 26 Aug 2014 at 7:24

[GoogleCodeExporter]

Similar issue, but with a different event...could you expose the dblclick event 
as well? This is especially useful when setting zoomToClick = false so click 
can be used to show info window.  Would be nice to attach the zoom to the 
dblclick event in that case.  

Original comment by nikhilso...@gmail.com on 28 Aug 2014 at 12:32