Original commit message from CVS:
- Reclaim cothread state even if the cothread was never activated after
the free.
- fix the bin state change when there are no more children.
- use a real method to signal the parent bin of a state change.
- move the state change policy in the scheduler.
- remove the unused and ridiculous state change event
- don't free the cothread state when the element is disabled. only free it
when the element is removed from the scheduler.