build gpg extension to use monkeysphere to validate hkps queries
gpg can query keyservers via plugin modules dropped into @/usr/lib/gnupg/gpgkeys_PROTO@
we should provide such a plugin that uses the monkeysphere to validate the certificate of the hkps keyserver.
Note that this could cause a nasty recursive query if we're not careful.
(from redmine: created on 2010-03-14, closed on 2010-12-08)