daemon: Internationalize guix-daemon.
* nix/nix-daemon/guix-daemon.cc (n_, _): New macros.
(guix_textdomain): New variable.
(doc): Use 'n_'.
(options): Likewise, and lowercase messages.
(argp): Add initializer for 'argp_domain' field.
(parse_opt): Use '_' for messages.
(main): Likewise, and add calls to 'setlocale', 'bindtextdomain', and
'textdomain'.
* daemon.am (guix_daemon_CPPFLAGS): Add -DLOCALEDIR.
* po/guix/Makevars (XGETTEXT_OPTIONS): Remove '--language' option. Add
'--keyword=n_'.
* po/guix/POTFILES.in: Add guix-daemon.cc.
7887bcbf56