title: SPListItemCollection.GetDataTable() doesn't return all columns?
body: <p>I ran into an issue when using the GetDataTable() method. I'm trying to return the default SharePoint column "FileRef" in my results to use. I include it in my SPQuery.ViewFields</p>
  
  <p>Query:</p>
  
  <pre><code>&lt;Where&gt;&lt;IsNotNull&gt;&lt;FieldRef Name='FileRef'/&gt;&lt;/IsNotNull&gt;&lt;/Where&gt;
  </code></pre>
  
  <p>ViewFields:</p>
  
  <pre><code>&lt;FieldRef Name='Title' /&gt;&lt;FieldRef Name='Category' /&gt;&lt;FieldRef Name='FileRef' /&gt;&lt;FieldRef Name='ID' /&gt;&lt;FieldRef Name='Created' /&gt;
  </code></pre>
  
  <p>I can even see it returned in the items.XML but when I call GetDataTable() it is not put in the datatable.</p>
  
  <pre><code>SPListItemCollection items = list.GetItems(spq);
  dtItems = items.GetDataTable();
  </code></pre>
  
  <p>Why isn't GetDataTable working correctly? Am I going to have to write my own conversion method?</p>