title: CheckboxCellEditor shows text and not a check box
body: <p>I'm using the following</p>
  
  <pre><code>org.eclipse.jface.viewers.CheckboxCellEditor.CheckboxCellEditor(Composite parent)
  </code></pre>
  
  <p>I'm creating a table viewer with cellEditors and doing the following</p>
  
  <pre><code>CellEditor[] editors = new CellEditor[columnNames.length];
  editors[7] = new CheckboxCellEditor(table);
  </code></pre>
  
  <p>I have a CellModifier that has the following</p>
  
  <pre><code>public Object getValue(Object element, String property) {
          Object result = null;
          ...
          result = Boolean.valueOf(task.isDfRequested());
          return result;
  }
  
   public void modify(Object element, String property, Object value) {
         item.isSelected(((Boolean)value).booleanValue());
  }
  </code></pre>
  
  <p>Finally I have a LabelProvider that has the following</p>
  
  <pre><code> public String getColumnText(Object element, int columnIndex) {
          String result = "";
          try { 
              result = Boolean.toString(item.isSelected());
          } catch (Exception ex) { } 
  
          break;
  </code></pre>
  
  <p>However, in my UI instead of having a check box I have the word true or false &amp;&amp; clicking it results in switching state to false or true.  Any ideas on why I don't have a checkbox??</p>