* use ScriptValueP, wrapped in AnyValue, instead of the specialized value types
 * serialize these values using script syntax.
 * However: #ifdefed out for now, because I first wanted to commit the following change:

This requires a change to handling of last_change of MultipleChoiceValue. Instead of storing it in the field, it is now just part of the action. The action therefore has to be passed to Value::update.