volunteers not removed from list of "all volunteers"

Just noticed a bug in function timeslots_signup_form_submit. Additional volunteers are added to the list of "all volunteers", but those who are removed from the schedule do not get removed from this list until/unless the node is edited and then function volunteer_timeslots_nodeapi rebuilds the list of all volunteers. So, a similar rebuilding needs to be implemented in function timeslots_signup_form_submit.