Make logging.c more readable by splitting up logging not implemented code path.
Make logging.c more readable by splitting up logging not implemented code path.

* logging.c
  (serf__log_init, serf__log_nopref, serf__log,
   serf_logging_create_stream_output, serf_logging_add_output): Define empty
  public functions when logging is not compiled-in.

jandre/serf,jandre/serf,jandre/serf,jandre/serf