Give question type a chance to upgrade it's attempts data upon editing a question

Since editing a questions with existing attetmpts should definitely be allowed, a question type should have a possibility to change attempt data to avoid breaks (and even try to save the students answers from corruption in some cases). This could be done by adding to a question type a function like

upgrade_existing_responses($oldquestion, $newquestion, $responses)

It is easy to implement in question engine and will add to quiz correctess and stability without restraining the user.