Bug 89031 [Undo/Redo] IWorkbench#getOperationSupport() marked experimental
IWorkbench#getOperationSupport() marked experimental
bundles/org.eclipse.core.commands/src/org/eclipse/core/commands/operations/DefaultOperationHistory.java
*/
	void internalRemove(IUndoableOperation operation) {
		operation.dispose();
		notifyRemoved(operation);
	}
	/*
	 * Notify listeners that an operation is about to execute.
	 */
	protected void notifyAboutToExecute(IUndoableOperation operation) {
		if (DEBUG_OPERATION_HISTORY_NOTIFICATION) {
			System.out.print("OPERATIONHISTORY >>> ABOUT_TO_EXECUTE ");  
			System.out.print(operation);
			System.out.println();
		}
		
		OperationHistoryEvent event = new OperationHistoryEvent(
				OperationHistoryEvent.ABOUT_TO_EXECUTE, this, operation);
		preNotifyOperation(operation, event);
		for (int i = 0; i < listeners.size(); i++)
			try {
				((IOperationHistoryListener) listeners.get(i))
					.historyNotification(event);
			} catch (Exception e) {
				handleNotificationException(e);
			}
	}
	/*
	 * Notify listeners that an operation is about to redo.
	 */
	protected void notifyAboutToRedo(IUndoableOperation operation) {