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
return null;
		
		NavigatorContentDescriptor src = (NavigatorContentDescriptor) contributionMemory.get(element);
		if (src != null)
			return src;
		return (NavigatorContentDescriptor) structuredViewerManager.getData(element);
	}
	/**
	 * 
	 */
	public static final boolean CONSIDER_OVERRIDES = true;
	
	/**
	 * Search for extensions that declare the given element in their
	 * <b>triggerPoints</b> expression.
	 * 
	 * @param anElement
	 *            The element to use in the query
	 * @param considerOverrides
	 * 
	 * @return The set of {@link INavigatorContentDescriptor}s that are
	 *         <i>visible</i> and <i>active</i> for this content service and
	 *         have a <b>triggerPoints</b> expression that is <i>enabled</i> for
	 *         the given element.
	 */
	public Set findDescriptorsByTriggerPoint(Object anElement, boolean considerOverrides) {
		
		
		NavigatorContentDescriptor descriptor = getSourceOfContribution(anElement);
		Set result = new TreeSet(ExtensionPriorityComparator.INSTANCE);