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/utmp-api.c

@@ -32,6 +32,7 @@
 # include <lite/lite.h>
 #endif
 
+#include "finit.h"
 #include "helpers.h"
 #include "util.h"
 #include "utmp-api.h"
@@ -174,7 +175,8 @@ int utmp_set_dead(int pid)
 
 static int encode(int lvl)
 {
-	if (!lvl) return 0;
+	if (lvl == INIT_LEVEL)
+		return 0;
 	return lvl + '0';
 }