ADMIN: New spamming highscore

This is depressing. Almost 100 spams to the lsh-list in 45 minutes,
which weren't tagged by the spamassassin installation in front of the
list server.

I guess I have no choice but to make the list posting policy members'
only, even if I *really* don't like that.

I'll make the same change to the nettle list, even if that list didn't
get the same volume of spam this time.

My sincere apologies to all subscribers.
/Niels