git-daemon: use LOG_PID, simplify logging code

git-daemon: use LOG_PID, simplify logging code

Make git-daemon use LOG_PID like most daemons, instead of prepending the
pid to the message ourselves, when using syslog(3).

Simplify the logging code by setting stderr to line buffered, instead of
building a single string and writing it out with a single write(2).

Give an extra log message at the daemon start-up.

Signed-off-by: Stephen R. van den Berg <srb@cuci.nl>
Signed-off-by: Junio C Hamano <gitster@pobox.com>