title: zoom_changed only triggers once in Google Maps API version 3 using MVC
body: <p>I'm trying to use the MVC objects in Google Maps version 3. What I can't seem to figure out is why my <code>zoom_changed</code> method is only invoked once. When I first load the map the <code>zoom_changed</code> method is invoked. But not when I zoom on the map.</p>
  
  <pre><code>function MarkerWidget (options) {
      this.setValues(options);
      this.set('zoom', this.map.zoom);
  
      var marker = new google.maps.Marker({
              icon : this.icon,
              mouseOverIcon : this.mouseOverIcon,
              orgIcon : this.orgIcon
      });
  
      marker.bindTo('map', this);
      marker.bindTo('position', this);
  
      google.maps.event.addListener(marker, 'mouseover', this.onmouseover);
      google.maps.event.addListener(marker, 'mouseout', this.onmouseout);
  }
  
  MarkerWidget.prototype = new google.maps.MVCObject();
  MarkerWidget.prototype.zoom_changed = function () {
      $.log(this, new Date());
  }
  </code></pre>
  
  <p>Shouldn't the map object fire the zoom event and notify all objects that has "this.set('zoom', this.map.zoom)"?</p>