Bug 32254 [Viewers] AbstractTreeViewer uses HashSet to remember expansion state
I20030216 The custom hash table should be used instead. Otherwise expansion state may be lost due to a different equals implementation of the element and the IElementComparer.
bundles/org.eclipse.jface/src/org/eclipse/jface/viewers/StructuredViewer.java
* </p>
	 * <p>
	 * Specifying which properties are affected may allow the viewer to optimize
	 * the update. For example, if the label provider is not affected by changes
	 * to any of these properties, an update may not actually be required.
	 * Specifing <code>properties</code> as <code>null</code> forces a full
	 * update of the given elements.
	 * </p>
	 * <p>
	 * If the viewer has a sorter which is affected by a change to one of the
	 * properties, the elements' positions are updated to maintain the sort
	 * order.
	 * </p>
	 * <p>
	 * If the viewer has a filter which is affected by a change to one of the
	 * properties, elements may appear or disappear if the change affects
	 * whether or not they are filtered out.
	 * </p>
	 * 
	 * @param elements
	 *            the elements
	 * @param properties
	 *            the properties that have changed, or <code>null</code> to
	 *            indicate unknown
	 */
	public void update(Object[] elements, String[] properties) {
		for (int i = 0; i < elements.length; ++i)
			update(elements[i], properties);
	}
	/**