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/finit.h

@@ -121,6 +121,7 @@ extern int    single;
 extern int    bootstrap;
 extern int    kerndebug;
 extern int    syncsec;
+extern int    readiness;
 extern char  *fstab;
 extern char  *sdown;
 extern char  *network;