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
* <code>ABOUT_TO_UNDO</code>, <code>ABOUT_TO_REDO</code>).
	 * Notifications for any other execute or add while this operation is open
	 * will not occur. Instead, those operations will be added to the current
	 * operation.
	 * </p>
	 * <p>
	 * Note: This method is intended to be used by legacy undo frameworks that
	 * do not expect related undo operations to appear in the same undo history
	 * as the triggering undo operation. When an operation is open, any
	 * subsequent requests to execute, add, undo, or redo another operation will
	 * result in that operation being added to the open operation. Once the
	 * operation is closed, the composite will be considered an atomic
	 * operation. Clients should not modify the composite directly (by adding
	 * and removing children) while it is open.
	 * </p>
	 * <p>
	 * When a composite is open, operations that are added to the history will
	 * be considered part of the open operation instead. Operations that are
	 * executed while a composite is open will first be executed and then added
	 * to the composite.
	 * </p>
	 * <p>
	 * Open operations cannot be nested. If this method is called when a
	 * different operation is open, it is presumed to be an application coding
	 * error and this method will throw an IllegalStateException.
	 * </p>
	 * 
	 * @param operation
	 *            the composite operation to be considered as the parent for all
	 *            subsequent operations.