title: ExtJS TabPanel missing scroll bar in ViewPort
body: <p>I have a ViewPort that I want to open a number of tabs.  One of my tabs is really long and should scoll off the bottom of the page.  However, the scrollbar is missing from the side.</p>
  
  <p>Here's my Viewport setup:</p>
  
  <pre><code>var viewport = new Ext.Viewport({
      layout:'border',
      enableTabScroll:true,
      deferredRender:true,
      items:[
          new Ext.BoxComponent({ // raw
              region:'north',
              el: 'north',
              height:32
          }),{
              region:'west',
              id:'west-panel',
              title:'West',
              split:true,
              width: 200,
              minSize: 175,
              maxSize: 400,
              collapsible: false,
              margins:'0 0 0 5',
              layout:'accordion',
              deferredRender: true,
              layoutConfig:{
                  animate:true
              },
              items: [{
                  contentEl: 'west',
                  title:'Navigation',
                  border:false,
                  collapsible: false,
                  iconCls:'nav'
              }]
          },
          new Ext.TabPanel({
              region:'center',
              id:'center',
              activeTab:0,
              items:[{
                  contentEl:'center1',
                  title: 'Close Me',
                  closable:true,
                  layout:'fit',
                  autoScroll:true
              }]
          })
       ]
  });
  </code></pre>
  
  <p>And here's my add tab code:</p>
  
  <pre><code>Ext.get("addplace").on('click', function() {
      centerTabs = Ext.getCmp('center');
      tab = centerTabs.add(new Ext.TabPanel({
          iconCls: 'tabs',
          id: 'add_place_tab',
          autoLoad: {url: '/admin/addplace', scripts : true,},
          title: 'Add Place',
          loadMask: false,
          closable:true
      }));
      centerTabs.setActiveTab(tab);
  });
  </code></pre>
  
  <p>Thanks in advance!</p>