title: Sort multiple columns sorting when clicking on a single column's head with DataTable
body: <p>I'm trying to sort 2 columns with the DataTable plugin for jQuery (latest version). With that, It's okay onload.</p>
  
  <pre><code> $('#example').dataTable( {
       "aaSorting": [ [2,'asc'], [3,'asc'] ],
  });
  </code></pre>
  
  <p>I have little difficulties to sort 2 columns on click. For exemple, when the user click on 'album', the table is not sorting the TrackNo column.
  My table looks like this:</p>
  
  <pre><code>-------------------------------------
  | Album             | TrackNo       |
  -------------------------------------
  | MyAlbum 2010      | 1 out of 12   |
  | MyAlbum 2010      | 9 out of 12   |
  | MyAlbum 2010      | 10 out of 12  |
  | MyAlbum 2010      | 4 out of 12   |
  | MyAlbum 2010      | 2 out of 12   |
  | MyAlbum 2010      | 12 out of 12  |
  -------------------------------------
  </code></pre>
  
  <p>Another problem is when I sort the column "Album", The TrackNo Column is sorted with this order: 1, 10, 12, 2, 4, 9. </p>
  
  <p>I've noticed that it's possible to change how DataTable sorts things with:</p>
  
  <pre><code>jQuery.fn.dataTableExt.oSort['numericstring-case-asc']  = function(x,y) {
      return ((x &lt; y) ? -1 : ((x &gt; y) ?  1 : 0));
  };
  
  jQuery.fn.dataTableExt.oSort['numericstring-case-desc'] = function(x,y) {
      return ((x &lt; y) ?  1 : ((x &gt; y) ? -1 : 0));
  };
  </code></pre>
  
  <p>My question is: how can I sort the TrackNo column so it will display tracks in the good order without adding a zero in front of each tracks?
  And how do I sort 2 columns on click?</p>