Bug 287103 [CommonNavigator] contentServiceLabelProvider doesn't properly implement overrides
bundles/org.eclipse.ui.navigator/src/org/eclipse/ui/internal/navigator/extensions/NavigatorContentDescriptorManager.java
VisibilityAssistant aVisibilityAssistant) {
		EvaluationCache c = (EvaluationCache) anEvaluationMap
				.get(aVisibilityAssistant);
		if (c == null) {
			anEvaluationMap.put(aVisibilityAssistant, c = new EvaluationCache(
					aVisibilityAssistant));
		}
		return c;
	}
	private boolean addDescriptorsConsideringOverrides(Object anElement,
			Set theChildDescriptors, VisibilityAssistant aVisibilityAssistant,
			Set theFoundDescriptors, boolean possibleChild) {
		int initialSize = theFoundDescriptors.size();
		NavigatorContentDescriptor descriptor;
		
		for (Iterator contentDescriptorsItr = theChildDescriptors.iterator(); contentDescriptorsItr
				.hasNext();) {
			descriptor = (NavigatorContentDescriptor) contentDescriptorsItr
					.next();
			boolean isApplicable = aVisibilityAssistant.isActive(descriptor)
					&& aVisibilityAssistant.isVisible(descriptor)
					&& (possibleChild ? descriptor.isPossibleChild(anElement) : descriptor.isTriggerPoint(anElement));
			if (descriptor.hasOverridingExtensions()) {
				boolean isOverridden;
				Set overridingDescriptors = new TreeSet(ExtensionPriorityComparator.INSTANCE);
				isOverridden = addDescriptorsConsideringOverrides(anElement, descriptor.getOverriddingExtensions(),
						aVisibilityAssistant, overridingDescriptors, possibleChild);
				if (!isOverridden && isApplicable) {
					theFoundDescriptors.add(descriptor);
				} else if (isOverridden) {