wip-hurd branch rebased on top of master

[Manolis Ragkousis]

Hello Guix,

I rebased the wip-hurd branch on top of master and I made sure we have the
same functionality as before.

There was a minor change I had to make in the first patch, in order to make
it work.
I am resending each patch so you can have a look. I am waiting for the okay
to push to wip-hurd. (delete old wip-hurd, push new one?).

This is necessary for two reason. First, make all the new guix
features available
to the hurd branch, so it's easier to work with and second make merging with
master, sometime in the future, easier.

Next are the patches.

Manolis