Export pid_file_set() function, useful to other subsystems as well

Rename, refactor, and export.

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

src/pid.h

@@ -32,6 +32,7 @@ int   pid_alive       (pid_t pid);
 char *pid_get_name    (pid_t pid, char *name, size_t len);
 
 char *pid_file        (svc_t *svc);
+int   pid_file_set    (svc_t *svc, char *file, int not);
 pid_t pid_file_read   (const char *fn);
 int   pid_file_create (svc_t *svc);
 int   pid_file_parse  (svc_t *svc, char *arg);