title: How to reload Ext.tree.TreePanel on demand?
body: <p>I want to create Ext.tree.TreePanel component and periodically load content from the external URl. So I've written something like</p>
  
  <pre><code> new Ext.tree.TreePanel({
          root: {
              nodeType: 'async',
              text: 'asdasd',
              draggable: false,
              id: 'folders-tree-root'
          },
          loader: new Ext.tree.TreeLoader()
  });
  </code></pre>
  
  <p>And now I want to reload this tree, so I write:</p>
  
  <pre><code>tree.loader.dataUrl = 'folders-sample.json';
  tree.root.reload();
  </code></pre>
  
  <p>And nothing happens.</p>
  
  <p><strong>add</strong>:
  The only way I've found is set some invalid value to <code>dataUrl</code> param on <code>TreeLoader</code> creation:</p>
  
  <pre><code> new Ext.tree.TreePanel({
          root: {
              nodeType: 'async',
              text: 'asdasd',
              draggable: false,
              id: 'folders-tree-root'
          },
          loader: new Ext.tree.TreeLoader(dataUrl: 'something')
  });
  </code></pre>