Fix #300: add ready:script for services, called when daemon is ready

In Finit a daemon can signal its readiness by creating/touching its PID
file.  An ancient UNIX concept -- a daemon creates its PID file when it
has set up signal handlers and is ready to receive IPC (signals), right
before entering its while(1) loop.

Finit took the concept a bit further, adding readiness signalling also
to daemon's by touching their PID file after having processed a SIGHUP.

For both these conditions Finit now supports a ready:script, called when
readiness is detected.  In later commits support for s6 and systemd
style readiness notification will be added that will hook the mechanism
implemented in this commit as well.

Signed-off-by: Joachim Wiberg <troglobit@gmail.com>

src/service.h

@@ -35,6 +35,8 @@ void      service_runtask_clean  (void);
 void      service_reload_dynamic (void);
 void      service_update_rdeps   (void);
 
+void      service_ready_script   (svc_t *svc); /* XXX: only for pidfile plugin before notify framework */
+
 int       service_timeout_after  (svc_t *svc, int timeout, void (*cb)(svc_t *svc));
 int       service_timeout_cancel (svc_t *svc);