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/AbstractTreeViewer.java
*           collect the elements
	 * @param widget
	 *           the widget
	 */
	private void internalCollectExpanded(List result, Widget widget) {
		Item[] items = getChildren(widget);
		for (int i = 0; i < items.length; i++) {
			Item item = items[i];
			if (getExpanded(item)) {
				Object data = item.getData();
				if (data != null)
					result.add(data);
			}
			internalCollectExpanded(result, item);
		}
	}
	/**
	 * Tries to create a path of tree items for the given element. This method
	 * recursively walks up towards the root of the tree and assumes that
	 * <code>getParent</code> returns the correct parent of an element.
	 * 
	 * @param element
	 *           the element
	 * @param expand
	 *           <code>true</code> if all nodes on the path should be
	 *           expanded, and <code>false</code> otherwise
	 * @return Widget
	 */
	protected Widget internalExpand(Object element, boolean expand) {
		if (element == null)