FAQ update

[David Relson]

Greetings,

I've done a bit of FAQ updating.  You can read the new version at
http://www.bogofilter.org/faq.php

Two FAQs have been added to "Operational Questions"

    * What is Unsure mode?
    * What does the '-u' (autoupdate) switch do?


Three FAQs have been moved from "Technical problems" to 
"Portability Problems":

    * How do I build bogofilter as non-root user or for
      a non-standard installation prefix?
    * How do I build bogofilter with patches?
    * How do I make the executables smaller?