[Evolution] Disable signature checking

[Lee Revell <rlrevell joe-job com>]

How can I completely disable GPG/PGP checking of signatures on every
message?  I think it's a performance problem on slower machines.
Browsing the message list seems to have become significantly slower
lately and I notice sometimes "Verifying message" takes a second or so.

I don't use this feature at all and I'd like to get some of my CPU
cycles back.

TIA,

Lee