New “guix refresh” command

[ludo@gnu.org (Ludovic Courtès)]

Hello!

There’s a new ‘guix refresh’ command.  The target audience is mostly
Guix developers: the command reports GNU packages that are not
up-to-date, and optionally updates the source files to reflect the new
version number and tarball hash.  (This is essentially a port of my
‘gnupdate’ program for Nixpkgs [0].)

When downloading new tarballs, it also retrieves signatures and checks
them with GPG, via the new (guix gnupg) module.  If the public key is
missing, it attempts to get it from keys.gnupg.net, and tries again; in
that case, the key is added to your keyring.  (It’s similar to what the
OpenSSH client does when introduced to new hosts.)

There’s room for improvement here and there, but the basic functionality
is in place, and it’s going to be profitable for the on-going round of
package updates.  :-)

Comments welcome!

Ludo’.

[0] http://thread.gmane.org/gmane.linux.distributions.nixos/3811