Bug 305703 [Viewers][CommonNavigator] remembered contributions can leak when using filters
bundles/org.eclipse.ui.navigator/src/org/eclipse/ui/internal/navigator/NavigatorContentService.java
* @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);
		
		
		Set possibleChildDescriptors = findDescriptorsWithPossibleChild(anElement, false);
		
		if (sourceDescriptor != null) {
			possibleChildDescriptors.add(sourceDescriptor);
		}
		for (Iterator iter = possibleChildDescriptors.iterator(); iter.hasNext();) {
			NavigatorContentDescriptor ncd = (NavigatorContentDescriptor) iter.next();
			findOverridingLabelExtensions(anElement, ncd, contributors);
		}
		
		return contributors;
	}
	private void findOverridingLabelExtensions(Object anElement,
			INavigatorContentDescriptor descriptor, LinkedHashSet contributors) {
		ListIterator iter = ((NavigatorContentDescriptor) descriptor).getOverridingExtensionsListIterator(false);
		while (iter.hasPrevious()) {
			INavigatorContentDescriptor child = (INavigatorContentDescriptor) iter.previous();
			if (assistant.isVisibleAndActive(child) && child.isPossibleChild(anElement)) {
				findOverridingLabelExtensions(anElement, child, contributors);
			}
		}
		contributors.add(getExtension(descriptor));
	}