title: jqGrid not sorting dates correctly
body: <p>I have an issue when sorting dates using <code>jqGrid</code>. Given the following dates</p>
  
  <p><code>jqGrid</code> is sorting my dates as follows:</p>
  
  <pre><code>01/01/2010
  01/01/2011
  01/02/2010
  01/02/2011
  </code></pre>
  
  <p>I would expect to see</p>
  
  <pre><code>01/01/2010
  01/02/2010
  01/01/2011
  01/02/2011
  </code></pre>
  
  <p>My date format is <code>dd/mm/yyyy</code> and I have the follow format options - </p>
  
  <pre><code>{
      name: 'myDate',
      index: 'myDate',
      sortable: true,
      sorttype: 'date'
  }
  </code></pre>
  
  <p>Have I missed something here or is this a limitation of the <code>jqGrid</code>?</p>