Fix #352: separate runlevel S from runlevel 0

Due to an old design decision runlevel S was encoded internally as '0',
meaning it was the same as halt/poweroff.  If you want to run scripts at
system shutdown this was less then ideal since it meant your scripts
also ran at bootstrap.

This change is quite invasive.  It introduces INIT_LEVEL (10) as the
value for runlevel S, meaning all code that parses and/or evaluates
anything for runlevel 0/S was affected and had to be reworked.

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

src/finit.c

@@ -60,7 +60,7 @@
 #include "utmp-api.h"
 #include "schedule.h"
 
-int   runlevel  = 0;		/* Bootstrap 'S' */
+int   runlevel  = INIT_LEVEL;	/* Bootstrap 'S' */
 int   cfglevel  = RUNLEVEL;	/* Fallback if no configured runlevel */
 int   cmdlevel  = 0;		/* runlevel override from cmdline */
 int   prevlevel = -1;