title: Scrollbar in treepanel extjs 4 not work
body: <p>I'm a problem with scrollbar in extjs 4.
  The horizontal scrollbars don't show and the vertical scrollbars don't move. I test the code in google chrome, IE and firefox. The javascript don't show errors.</p>
  
  <p>This is a part of code, in productos_panel is the problem:</p>
  
  <pre class="lang-js prettyprint-override"><code>{
      xtype: 'container',
      id: 'panel_side_bar',
      margin: 5,
      width: 250,
      autoScroll:true,
      layout: {
          type: 'border'
      },
      region: 'west',
      items: [
          {
              xtype: 'treepanel',
              id: 'productos_panel',
              title: 'Listado de Productos',
              rootVisible:false,
              autoScroll : true,
              region: 'center',
              root: getDirectJSON("&lt;?php echo url_for("@get_categoria_prod",true)?&gt;"),
              viewConfig: {
                  id: 'productos'
              },
              listeners: {
                  itemclick: {
                          fn: evtClickItemTree
                  }
              }
          },
          {
              xtype: 'container',
              height: 51,
              id: 'botonera',
              layout: {
                  type: 'vbox'
              },
              region: 'north',
              items: [
                  text_input_filtro,
                  {
                      xtype: 'container',
                      id: 'contenedor_btns_filtro',
                      height: 25,
                      width:250,
                      layout: {
                          type: 'hbox'
                      },
                      items: [
                          {
                              xtype: 'button',
                              id: 'button_filtrar',
                              text: 'Filtrar',
                              handler: evtButtonFiltrar,
                              flex: 1
                          },
                          {
                              xtype: 'button',
                              id: 'button_mostrar_todo',
                              text: 'Mostrar Todo',
                              handler: evtButtonMostrarTodo,
                              flex: 1
                          }
                      ]
                  }
              ]
          }
  </code></pre>
  
  <p>Thanks for all.</p>