title: Custom column sorting in Dojo Datagrid programmatically
body: <p>I have created a <code>dojox.grid.datagrid</code> programmatically and I need custom sorting on the columns.
  For this I tried using <code>ItemFileWriteStore.comparatorMap['field'] = comparatorFunc</code>. But my comparator function is never called.</p>
  
  <p>Any idea on what I am missing here?</p>