- Set config_file to a default filename if it is NULL.

- Set config_file to a default filename if it is NULL.
- Changed create_pid_file() to fail if the pidfile already exists,
  which makes the daemon exit with an error.
- Output errors about a failure to open the config file or the lock
  file to (a still open) stderr.
- We now notice (and complain) if fork() fails.