title: TableColumnExt not respecting prototype value
body: <p>I'm trying to use SwingX's <code>TableColumnExt</code> class to set a prototype value for the column's width in the hierarchical column of a <code>JXTreeTable</code>. After I initialize the model and table I do this:</p>
  
  <pre><code>TableColumnExt column = dataTable.getColumnExt(0);            
  column.setPrototypeValue(500);
  </code></pre>
  
  <p>When my table is rendered, all columns are equally sized. These are the methods I'm using on the <code>JXTreeTable</code> instance.</p>
  
  <pre><code>dataTable.setRowHeight(28);
  dataTable.setFillsViewportHeight(true);
  dataTable.setHorizontalScrollEnabled(true);
  </code></pre>
  
  <p>What am I doing wrong here?</p>