CONFIG_PID_FILE_PATH: new configuration option for pidfile paths

CONFIG_PID_FILE_PATH: new configuration option for pidfile paths

We set a default path for the directory where pidfiles are create
when FEATURE_PIDFILE is selected.  The default has no effect on
applets which must specify a pidfile path on the command line to
run, and it can be overridden by applets which optionally allow
the user to specify the pidfile path.

We also add pidfile write/remove support for klogd, ntpd and watchdog.
For syslogd, we add a missing remove_pidfile() for better cleanup
on daemon exit.

Signed-off-by: Anthony G. Basile <blueness@gentoo.org>
Signed-off-by: Mike Frysinger <vapier@gentoo.org>