Changed list access policies

[Josh Petrie]

I have removed the restriction that members need to be approved to
join the list; anybody can sign up now without requiring intervention
from one of the administrators. Membership is still required to post,
though. The list is also searchable via the web interface for Google
Groups.

I'm pretty sure we won't get spammed this way, but we can always
change it back if it becomes a problem.

-- jmp