auto-update in 0.16.2

[David Relson]

Stefan,

Let me explain the change in '-u'.  Recently I took a look at the scores
of messages that were being registered when '-u' was in use.  Over 90%
of them were "obvious" ham or spam, i.e. ham with scores < 0.01 or spam
with scores > 0.99.  Since the messages were so easily categorized, it
seems that there's little value in using them for training.  Introducing
a config file option "thresh_update=0.01" and a corresponding command
line option "-u 0.01" seemed the obvious way of dealing with this. 
Cutting the number of wordlist updates has the dual benefits of making
bogofilter faster and slowing the growth of the database.  I thought it
a worthwhile addition :-)

Cheers!

David