configurable greylisting time about gross HOT 4 CLOSED

This can be done, but is it really worth the effort? I have tested different 
times and have not seen any relevant 
performance gain with longer greylisting times.

Hmm. If greylisting with tools like gross will be prominent amongst all MTAs of 
the Internet forces spammers to 
adapt their methods, this could come a handy option in years to come. But, I 
think this is past 1.0 stuff unless 
the short time is proven to be inefficient.

I've seen that spammers have started stupidly firing off 2 messages, one right 
after
another.  This setting could prevent the second message from getting through.

Obviously this setting should be used with caution, especially if you are 
greylisting
non-suspicious-senders too.

There is now a 10 second delay before filters are updated. It could be longer, 
especially if you are running a 
replicated pair of grossd's. I'll make it a configurable parameter.

The configuration file now takes option greylist_delay that allows configuring 
the delay.