Hi Guix!

While investigating an issue I have with dovecot and knot, I figured
that the dovecot service had a custom mkdir-p/perms procedure that
hard-coded the directory to chown, which would not chown any other
directories created with it. The patch makes it use mkdir-p/perms from
(gnu build utils) instead. I don't think this will fix my issue, but at
least, that's one bug fixed :)