New option --config and --no-config for the daemon.

* src/payprocd.c (main): Make LOGFILE file global.  Factor option
parser out to ...
(parse_options): new.  Add config file parser.
(launch_server): Do not fork with --no-detach.

We will soon need a couple more configuration options and thus a
config file will be very helpful

• Signed-off-by: Werner Koch <wk@gnupg.org>