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.ui.navigator/src/org/eclipse/ui/internal/navigator/NavigatorContentService.java
if (rootContentProviders == null) {
				rootContentProviders = extractContentProviders(findRootContentExtensions(anElement));
			}
		}
		return rootContentProviders;
	}
	
	/**
	 * Returns the list of extensions that should be considered as possible
	 * contributors of CNF artifacts (labels, sorters, ...). The algorithm
	 * first considers the source of contribution and its overrides, and then
	 * any possibleChildren and their overrides in order.
	 * 
	 * @param anElement
	 *            An element from the tree (any element contributed to the
	 *            tree).
	 * @return A Collection of NCEs sorted in the correct order for label provider application
	 */
	public Collection findPossibleLabelExtensions(Object anElement) {
		LinkedHashSet contributors = new LinkedHashSet();
		INavigatorContentDescriptor sourceDescriptor = getSourceOfContribution(anElement);
		
		if (sourceDescriptor != null) {
			findOverridingLabelExtensions(anElement, sourceDescriptor, contributors);
		}
		
		
		Set possibleChildDescriptors = findDescriptorsWithPossibleChild(anElement, false);
		for (Iterator iter = possibleChildDescriptors.iterator(); iter.hasNext();) {
			NavigatorContentDescriptor ncd = (NavigatorContentDescriptor) iter.next();