title: How do I use the 'concat' type in the addColumn() method when building a grid?
body: <p>Mage/Adminhtml/Widget/Grid/Column/Renderer/Concat.php -- can someone please provide an example of its usage? For instance, can it be used in place of:</p>
  
  <pre><code>$this-&gt;addColumn('order_item', array(
    'header'=&gt; $this-&gt;__('Order # (Item #)'),
    'sortable'=&gt; true,
    'index'=&gt; 'order_item',
    'filter_index'=&gt; "CONCAT(orders.increment_id, ' (', main_table.item_id, ')')",
    'width'=&gt; '140px',
  ));
  </code></pre>