Since MPD switches user, the pid-file must be in a writable dir. This
is now always /var/run/mpd/(user)/pid.
* gnu/services/audio.scm (mpd-service-type): Add a activation-service
extension.
(<mpd-configuration>)[pid-file]: Remove.
(mpd-service): Rename to...
(mpd-shepherd-service): ... this.
(mpd-file-name, mpd-service-activation): New procedure.
* doc/guix.texi (Audio Services): Document the changes.
Signed-off-by: Ludovic Courtès <ludo@gnu.org>
b6dc69af1d