Indicate that there is a problem with what the user has (or has not)
input, such that the Next/Finish buttons should be disabled until the
user has made some change.
Called when the number or names of the steps of the
wizard changes (for example, the user made a choice in one pane which
affects the flow of subsequent steps).
Object which may be returned from WizardPage.WizardResultProducer.finish()
or WizardPanelProvider.finish(), or passed to
DeferredWizardResult.ResultProgressHandle.finish().