#106 temporary members, delivery disable on cc

[Paul Wise]

when lists are open to non-members - either through
admin approval, orfully open it would be nice if mailman
could then deliver the rest of the thread initiated by that
non-member to that non-member. this would need some
kind of password for the non-member to turn off delivery,
and a way for admins to also do this.

related to this would be the ability to turn off delivery to
email addresses that are listed as bcc/cc/to on arrival,
this would prevent people from recieving duplicate posts,
especially usefull for people who are used to the old
behaviour of mailman (no temp members), who cc by
habit