[ubl] Again checking list presence

Oops, sorry, I didn't do that right.  What I should have said was:

Everyone who receives this message (posted to )
should also have recently received a welcome message from the
ubl-comment list.  If you did not get a copy of the welcome message
from ubl-comment, you should subscribe to the ubl-comment list so that
you can see what the world in general has to say about what we're
doing.

Jon