title: gwt problem with HandlerRegistration
body: <p>I have a problem. 
  I have a map and added ClickHandler, but after pushing a button I want to remove it. I know that there's some HandlerRegistration but I don't know how to use it.
  part of my code:</p>
  
  <pre><code>map.addMapClickHandler(new MapClickHandler()
  
          {
              public void onClick(MapClickEvent e) 
              {
                   ...
                  }
          });
  </code></pre>
  
  <p>can anyone help me?</p>