Bug 121034 [jar import] Cancel should undo all already executed refactorings
3.2 M4
org.eclipse.ltk.ui.refactoring/src/org/eclipse/ltk/ui/refactoring/history/RefactoringHistoryWizard.java
* Returning a status of severity {@link RefactoringStatus#FATAL} will
	 * terminate the execution of the refactorings.
	 * </p>
	 * 
	 * @param monitor
	 *            the progress monitor to use
	 * 
	 * @return a status describing the outcome of the operation
	 */
	protected RefactoringStatus aboutToPerformHistory(final IProgressMonitor monitor) {
		Assert.isNotNull(monitor);
		return new RefactoringStatus();
	}
	/**
	 * Hook method which is called before the a refactoring of the history is
	 * executed. The refactoring itself is in an initialized state at the time
	 * of the method call. The default implementation does nothing and returns a
	 * status of severity {@link RefactoringStatus#OK}. This method may be
	 * called from non-UI threads.
	 * <p>
	 * Subclasses may extend this method to perform any special processing.
	 * </p>
	 * <p>
	 * Returning a status of severity {@link RefactoringStatus#FATAL} will
	 * terminate the execution of the current refactoring.
	 * </p>
	 * 
	 * @param refactoring
	 *            the refactoring about to be executed
	 * @param descriptor