uscan: enable use of SOP (allows verification of multiple signatures, addressing https://bugs.debian.org/1010955)
This series solves https://bugs.debian.org/1010955 by permitting the use of any Stateless OpenPGP Command Line Interface ("SOP") implementation, of which there are currently three in debian unstable.
It also removes the need for uscan
to invoke gpg
just for the sake of armoring and dearmoring OpenPGP material.