Do not issue temporary reject when spamd is unavailable.

Previously I was using the http://marc.merlins.org/linux/exim/sa.html patch to 
have SpamAssassin reject messages at run time.  I upgraded exim and switched to 
using exiscan for doing this last week.

However, I now notice that if exiscan cannot contact spamd, it issues a 
temporary rejection.  Can I change that?  If not, I may have to go back to the 
other system.  Exim's more reliable then SpamAssassin.  If our spam filtering 
fails for a bit, such as over a weekend, while that's annoying, it wouldn't be 
a big deal.  But no e-mail during that period?  That would be considered a 
problem.