title: How to order by multiple columns with propel
body: <p>I need to sort a query by 2 columns. Is this possible using propel?</p>
  
  <p>i tried:</p>
  
  <pre><code>$c-&gt;addAscendingOrderByColumn(self::COL1);
  $c-&gt;addAscendingOrderByColumn(self::COL2);
  </code></pre>
  
  <p>but the second call to addAscendingOrderByColumn overrides the first one.</p>
  
  <p>Regards,
  Radu.</p>