Bug 135284 [Viewers] API: need to add methods to StructuredViewer to support ViewerComparator
bundles/org.eclipse.jface/src/org/eclipse/jface/viewers/StructuredViewer.java
/**
	 * A map from the viewer's model elements to SWT widgets. (key type:
	 * <code>Object</code>, value type: <code>Widget</code>).
	 * <code>null</code> means that the element map is disabled.
	 */
	private CustomHashtable elementMap;
	/**
	 * The comparer to use for comparing elements, or <code>null</code> to use
	 * the default <code>equals</code> and <code>hashCode</code> methods on
	 * the element itself.
	 */
	private IElementComparer comparer;
	/**
	 * This viewer's sorter. <code>null</code> means there is no sorter.
	 */
	private ViewerSorter sorter;
	/**
	 * This viewer's filters (element type: <code>ViewerFilter</code>).
	 * <code>null</code> means there are no filters.
	 */
	private List filters;
	/**
	 * Indicates whether a selection change is in progress on this viewer.
	 * 
	 * @see #setSelection(ISelection, boolean)
	 */
	private boolean inChange;
	/**
	 * Used while a selection change is in progress on this viewer to indicates
	 * whether the selection should be restored.