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 element
	 *           the element
	 * @return <code>true</code> if the node is expanded, and <code>false</code>
	 *         if collapsed
	 */
	public boolean getExpandedState(Object element) {
		Assert.isNotNull(element);
		Widget item = findItem(element);
		if (item instanceof Item)
			return getExpanded((Item) item);
		return false;
	}
	/**
	 * Returns the number of child items of the given SWT control.
	 * 
	 * @param control
	 *           the control
	 * @return the number of children
	 */
	protected abstract int getItemCount(Control control);
	/**
	 * Returns the number of child items of the given SWT item.
	 * 
	 * @param item
	 *           the item
	 * @return the number of children
	 */
	protected abstract int getItemCount(Item item);
	/**