morebits: misc. amendments to QuickForm

- The custom event on radios and checkboxes now fires after the
  subgroup is created, meaning that the custom event has access to the
  subgroup's controls
- And yes, the subgroup does need to be cloned!

These are in relation to an upcoming overhaul of twinklespeedy.
morebits: fix the amendments to QuickForm

Sorry about this. This bit of code is really quite subtle, and I missed
the point in the last commit. But I think I've finally fixed it once and
for all. Let's hope!