Bug 305703 [Viewers][CommonNavigator] remembered contributions can leak when using filters
bundles/org.eclipse.jface/src/org/eclipse/jface/viewers/AbstractTreeViewer.java
*            the item
	 * @return the previous item, or <code>null</code> if none
	 */
	protected Item getPreviousItem(Item item) {
		
		
		Item parent = getParentItem(item);
		if (parent == null) {
			return null;
		}
		Item[] siblings = getItems(parent);
		if (siblings.length == 0 || siblings[0] == item) {
			return parent;
		}
		Item previous = siblings[0];
		for (int i = 1; i < siblings.length; i++) {
			if (siblings[i] == item) {
				return rightMostVisibleDescendent(previous);
			}
			previous = siblings[i];
		}
		return null;
	}
	
	protected Object[] getRawChildren(Object parentElementOrTreePath) {
		boolean oldBusy = isBusy();
		setBusy(true);
		try {
			Object parent;
			TreePath path;