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/private.h

@@ -32,6 +32,8 @@
 #define MATCH_CMD(l, c, x) \
 	(!strncasecmp(l, c, strlen(c)) && (x = (l) + strlen(c)))
 
+#define IS_RESERVED_RUNLEVEL(l) (l == 0 || l == 6 || l == INIT_LEVEL)
+
 extern char *finit_conf;
 extern char *finit_rcsd;
 extern svc_t *wdog;