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
* @param parent
	 *           the parent widget
	 * @param element
	 *           the element
	 * @param index
	 *           if non-negative, indicates the position to insert the item
	 *           into its parent
	 */
	protected void createTreeItem(Widget parent, Object element, int index) {
		Item item = newItem(parent, SWT.NULL, index);
		updateItem(item, element);
		updatePlus(item, element);
	}
	/**
	 * The <code>AbstractTreeViewer</code> implementation of this method also
	 * recurses over children of the corresponding element.
	 */
	protected void disassociate(Item item) {
		super.disassociate(item);
		
		
		
		if (usingElementMap())
			disassociateChildren(item);
	}
	/**
	 * Disassociates the children of the given SWT item from their
	 * corresponding elements.
	 * 
	 * @param item