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
* Search for extensions that declare the given element in their
	 * <b>possibleChildren</b> expression.
	 * 
	 * @param anElement
	 *            The element to use in the query
	 * @return The set of {@link INavigatorContentExtension}s that are
	 *         <i>visible</i> and <i>active</i> for this content service and
	 *         have a <b>possibleChildren</b> expression that is <i>enabled</i>
	 *         for the given element.
	 */
	public Set findOverrideableContentExtensionsForPossibleChild(
			Object anElement) {
		Set overrideableExtensions = new TreeSet(
				ExtensionPriorityComparator.INSTANCE);
		Set descriptors = findDescriptorsWithPossibleChild(anElement, false);
		for (Iterator iter = descriptors.iterator(); iter.hasNext();) {
			INavigatorContentDescriptor descriptor = (INavigatorContentDescriptor) iter
					.next();
			if (descriptor.hasOverridingExtensions()) {
				overrideableExtensions.add(getExtension(descriptor));
			}
		}
		return overrideableExtensions;
	}
	/*
	 * (Non-Javadoc)
	 * 
	 * @see INavigatorContentService#getContentDescriptorById(String)
	 */
	public INavigatorContentDescriptor getContentDescriptorById(