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.h

@@ -63,10 +63,11 @@
 #define LINE_SIZE               1024
 #define BUF_SIZE                4096
 
-/* We extend the INIT_CMD_ range for the new initctl tool. */
 #define INIT_SOCKET             _PATH_VARRUN "finit/socket"
 #define INIT_MAGIC              0x03091969
+#define INIT_LEVEL              10
 
+/* We extend the INIT_CMD_ range for the new initctl tool. */
 #define INIT_CMD_START          0
 #define INIT_CMD_RUNLVL         1
 #define INIT_CMD_POWERFAIL      2