Bug 299438 [CommonNavigator] CNF viewer state non properly reset when NCEs are activated or deactivated
The map of the objects to the NCEs should be reset whenever the NCEs associated with the viewer to change to avoid having stale label information. This has shown up when looking at the CNF tests that change the viewer.
bundles/org.eclipse.jface/src/org/eclipse/jface/viewers/StructuredViewer.java
* 
	 * @param sorter
	 *            a viewer sorter, or <code>null</code> if none
	 */
	public void setSorter(ViewerSorter sorter) {
		if (this.sorter != sorter) {
			this.sorter = sorter;
			refresh();
		}
	}
	/**
	 * Sets this viewer's comparator to be used for sorting elements, and triggers refiltering and 
	 * resorting of this viewer's element.  <code>null</code> turns sorting off.
	 * To get the viewer's comparator, call <code>getComparator()</code>.
     * <p>
     * IMPORTANT: This method was introduced in 3.2. If a reference to this viewer object 
     * is passed to clients who call <code>getSorter()<code>, null may be returned from
     * from that method even though the viewer is sorting its elements using the
     * viewer's comparator.
     * </p>
	 * 
	 * @param comparator a viewer comparator, or <code>null</code> if none
     *
     * @since 3.2
	 */
	public void setComparator(ViewerComparator comparator){
		if (this.sorter != comparator){
			this.sorter = comparator;
			refresh();
		}