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/DefaultOperationHistory.java
Assert.isNotNull(operation);
		IStatus status;
		if (operation.canRedo()) {
			status = getRedoApproval(operation, info);
			if (status.isOK()) {
				status = doRedo(monitor, info, operation);
			}
		} else {
			if (DEBUG_OPERATION_HISTORY_UNEXPECTED) {
				Tracing.printTrace("OPERATIONHISTORY", 
						"Redo operation not valid - " + operation); 
			}
			status = IOperationHistory.OPERATION_INVALID_STATUS;
		}
		return status;
	}
	/*
	 * (non-Javadoc)
	 * 
	 * @see org.eclipse.core.commands.operations.IOperationHistory#removeOperationApprover(org.eclipse.core.commands.operations.IOperationApprover)
	 */
	public void removeOperationApprover(IOperationApprover approver) {
		approvers.remove(approver);
	}
	/*
	 * (non-Javadoc)
	 * 
	 * @see org.eclipse.core.commands.operations.IOperationHistory#removeOperationHistoryListener(org.eclipse.core.commands.operations.IOperationHistoryListener)
	 */
	public void removeOperationHistoryListener(