[MlMt] Sign by default Based on history not working?

[Eric Sharakan]

Running r5579, I'm finding MM is not making correct decisions on whether 
to sign my emails or not.  I have 5 accounts, two with S/MIME signing 
certs and three without.  It used to be that setting Sign by default to 
"Based on history", mails I compose on the two accounts with email 
signing certs would be signed and mail from others accounts would not.

Now it seems to simply remember whether I signed the last message or not 
and repeat that, so as I switch accounts it's often making the wrong 
decision.  And if I set it to "Always", it throws an error when I try to 
send from an account with no cert.

I guess what I want is a "Based on existence of valid cert" setting. :-)

-Eric