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
public static final IUndoContext GLOBAL_UNDO_CONTEXT = new GlobalUndoContext();
	/**
	 * An operation info status describing the condition that there is no
	 * available operation for redo.
	 */
	public static final IStatus NOTHING_TO_REDO_STATUS = new OperationStatus(
			IStatus.INFO, OperationStatus.DEFAULT_PLUGIN_ID,
			OperationStatus.NOTHING_TO_REDO, "No operation to redo", null); 
	/**
	 * An operation info status describing the condition that there is no
	 * available operation for undo.
	 */
	public static final IStatus NOTHING_TO_UNDO_STATUS = new OperationStatus(
			IStatus.INFO, OperationStatus.DEFAULT_PLUGIN_ID,
			OperationStatus.NOTHING_TO_UNDO, "No operation to undo", null); 
	/**
	 * An operation error status describing the condition that the operation
	 * available for execution, undo or redo is not in a valid state for the
	 * action to be performed.
	 */
	public static final IStatus OPERATION_INVALID_STATUS = new OperationStatus(
			IStatus.ERROR, OperationStatus.DEFAULT_PLUGIN_ID,
			OperationStatus.OPERATION_INVALID, "Operation is not valid", null); 
	/**
	 * <p>
	 * Add the specified operation to the history without executing it. The
	 * operation should have already been executed by the time it is added to
	 * the history. Listeners will be notified that the operation was added to
	 * the history (<code>OPERATION_ADDED</code>).
	 * </p>