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/TreeViewer.java
* This viewer's control.
	 */
	private Tree tree;
/**
 * Creates a tree viewer on a newly-created tree control under the given parent.
 * The tree control is created using the SWT style bits <code>MULTI, H_SCROLL, V_SCROLL,</code> and <code>BORDER</code>.
 * The viewer has no input, no content provider, a default label provider, 
 * no sorter, and no filters.
 *
 * @param parent the parent control
 */
public TreeViewer(Composite parent) {
	this(parent, SWT.MULTI | SWT.H_SCROLL | SWT.V_SCROLL | SWT.BORDER);
}
/**
 * Creates a tree viewer on a newly-created tree control under the given parent.
 * The tree control is created using the given SWT style bits.
 * The viewer has no input, no content provider, a default label provider, 
 * no sorter, and no filters.
 *
 * @param parent the parent control
 * @param style the SWT style bits used to create the tree.
 */
public TreeViewer(Composite parent, int style) {
	this(new Tree(parent, style));
}
/**
 * Creates a tree viewer on the given tree control.
 * The viewer has no input, no content provider, a default label provider, 
 * no sorter, and no filters.