[Mimedefang] Disabling AV checks by $RelayAddr

[Justin Shore]

I'm having trouble figuring out how to disable AV checks for a handle of
IPs.  I already do this for SpamAssassin checks.  I can't decide if this
code should go into message_contains_virus or entity_contains_virus.  I've 
been looking through the man pages and just can't decide which one (or 
both) should contain the IP checking code.  Any suggestions?

BTW, MD hasn't gone wacko yet today.  I'm bouncing some spamtrap mail 
through it now to generate extra traffic.  I'm trying to eliminate the AV 
checking on localhost which is adding to my load.  Thanks

Justin