title: ExtJS - Custom Column Renderer on TreeGrid isn't being fired
body: <p>I have an ExtJS TreeGrid and I'm trying to add a custom renderer to a particular column. Unfortunately it's not working - the event isn't being fired and no warnings are given off. I couldn't find the API for the TreeGrid either. Has anyone else experienced this?</p>
  
  <p>Here's the code:</p>
  
  <pre><code>    var tree = new Ext.ux.tree.TreeGrid({
          title: 'My Tree Grid',
          loader: treeLoader,
          columns:[{
              header: 'Title',
              dataIndex: 'title',
              width: 500
          },{
              header: 'Testing',
              width: 100,
              dataIndex: 'testing',
              renderer: function(value) {
                console.log('Test');
              },
              align: 'center'
          }]
       });
  </code></pre>
  
  <p>Thanks!</p>