initctl: Add SysV compat support for setenv

- Fix compat INIT_CMD_ defines so Finit clients can talk to SysV init
- Add setenv support, only for INIT_HALT={POWERDOWN,HALT} to runlevel 6

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

sig.h

@@ -55,6 +55,11 @@
                 sigaction(sig, &sa, NULL);      \
         } while (0)
 
+/*
+ * For old-style /dev/initctl shutdown we default to halt
+ */
+#define SHUT_DEFAULT SHUT_HALT
+
 typedef enum {
 	SHUT_OFF,
 	SHUT_HALT,