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
* Returns whether an attempt should be made to preserve selection across
	 * update operations. To be used by subclasses that override
	 * {@link #preservingSelection(Runnable)}.
	 * 
	 * @return <code>true</code> if selection should be preserved,
	 *         <code>false</code> otherwise
	 */
	boolean getPreserveSelection() {
		return this.preserveSelection;
	}
	/**
	 * Hook for testing.
	 * @param element
	 * @return Widget
	 */
	public Widget testFindItem(Object element) {
		return findItem(element);
	}
	/**
	 * Hook for testing.
	 * @param element
	 * @return Widget[]
	 * @since 3.2
	 */
	public Widget[] testFindItems(Object element) {
		return findItems(element);
	}
	
	/**
	 * Removes all elements from the map.