Add 'notify:pid' style readiness notifaction and 'readiness none'

This change expands the readiness notification system in Finit with the
native 'pid' style, which will remain the default readiness in Finit 4.x

For systems that want to transition to Finit 5.x early, a global option
to set 'readiness none' in /etc/finit.conf, has been added.  This change
the service default notification mode to 'notify:none', which can also
be set by Finit 4.x ('readiness pid') for select services.

Fixes #386.

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

src/svc.h

@@ -83,6 +83,14 @@ typedef enum {
 	SVC_ONCRASH_SCRIPT,
 } svc_oncrash_action_t;
 
+/* 0: none, 1: systemd, 2: s6 */
+typedef enum {
+	SVC_NOTIFY_NONE = 0,
+	SVC_NOTIFY_PID,
+	SVC_NOTIFY_SYSTEMD,
+	SVC_NOTIFY_S6,
+} svc_notify_t;
+
 #define MAX_ID_LEN       16
 #define MAX_ARG_LEN      64
 #define MAX_CMD_LEN      256
@@ -202,7 +210,7 @@ typedef struct svc {
 	/*
 	 * Readiness notification socket: systemd, s6
 	 */
-	int	       notify;	       /* 0: none, 1: systemd, 2: s6 */
+	svc_notify_t   notify;
 	uev_t	       notify_watcher; /* i/o watcher */
 
 	/* time at svc_del(), used by gc timer */