Bug 123316 [Undo] - API BEHAVIOR - should always place a successfully undone/redone op on the redo/undo history
bundles/org.eclipse.core.commands/src/org/eclipse/core/commands/operations/IOperationHistory.java
* @param mode
	 *            the mode the operation is executing in. Can be one of
	 *            <code>EXECUTE</code>, <code>UNDO</code>, or
	 *            <code>REDO</code>. This determines what notifications are
	 *            sent.
	 */
	void openOperation(ICompositeOperation operation, int mode);
	/**
	 * <p>
	 * The specified operation has changed in some way since it was added to the
	 * operation history. Notify listeners with an OPERATION_CHANGED event.
	 * </p>
	 * 
	 * @param operation
	 *            the operation that has changed.
	 * 
	 */
	void operationChanged(IUndoableOperation operation);
	/**
	 * <p>
	 * Get the operation that will next be undone in the given undo context.
	 * </p>
	 * 
	 * @param context
	 *            the context for the undo
	 * @return the operation to be undone or <code>null</code> if there is no
	 *         operation available. There is no guarantee that the available
	 *         operation is valid for the undo.
	 */
	IUndoableOperation getUndoOperation(IUndoContext context);