supervise-daemon: multiple fixes

- Harden against dying by handling all signals that would terminate the
program and adding --reexec support
- factor the supervisor into its own function
- fix test for whether we are already running

src/includes/rc-misc.h

@@ -47,6 +47,7 @@ bool rc_conf_yesno(const char *var);
 void env_filter(void);
 void env_config(void);
 int signal_setup(int sig, void (*handler)(int));
+int signal_setup_restart(int sig, void (*handler)(int));
 int svc_lock(const char *);
 int svc_unlock(const char *, int);
 pid_t exec_service(const char *, const char *);