title: How add in Ext.LoadMask Ext.Button?
body: <p>Only work like:</p>
  
  <pre><code>     mask_grid_navi_via_points = new Ext.LoadMask(grid_navi_via_points.getEl(), {msg: 'Text...&lt;button&gt;Cancel&lt;/button&gt;'});
  </code></pre>
  
  <p>I want insert Ext.Button and if like:</p>
  
  <pre><code>     var btn = new Ext.Button({
          renderTo: id,
          text: 'Cancel',
          handler: function(){
                      mask_grid_navi_via_points.hide();
          }
       });
       mask_grid_navi_via_points = new Ext.LoadMask(grid_navi_via_points.getEl(), {msg: 'Text...'+btn});
  </code></pre>
  
  <p>return [object Object]?</p>