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 The set of {@link INavigatorContentExtension}s that are
	 *         <i>visible</i> and <i>active</i> for this content service and
	 *         either declared through a
	 *         <b>org.eclipse.ui.navigator.viewer/viewerContentBinding</b> to be
	 *         a root element or have a <b>triggerPoints</b> expression that is
	 *         <i>enabled</i> for the given element.
	 */
	public Set findRootContentExtensions(Object anElement) {
		return findRootContentExtensions(anElement, 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 toRespectViewerRoots
	 *            True respect the <b>viewerContentBinding</b>s, False will look
	 *            only for matching <b>triggerPoints</b> expressions.
	 * @return The set of {@link INavigatorContentExtension}s that are
	 *         <i>visible</i> and <i>active</i> for this content service and
	 *         either declared through a
	 *         <b>org.eclipse.ui.navigator.viewer/viewerContentBinding</b> to be
	 *         a root element or have a <b>triggerPoints</b> expression that is
	 *         <i>enabled</i> for the given element.
	 */
	public Set findRootContentExtensions(Object anElement,
			boolean toRespectViewerRoots) {
		SortedSet rootExtensions = new TreeSet(
				ExtensionSequenceNumberComparator.INSTANCE);