Fix incorrect use of variable arguments in run_parts() and simplify code

The run_parts() implementation used variable arguments in a bad way,
resulting in it not working properly.  Replaced va_*() code with a
simple cmd argument that's passed to each script called.

Also, the opendir()/readdir() code has been replaced with scandir()
using regular alphasort(). This simplifies the code somewhat as well.

Otherwise, minor cleanups.

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

helpers.h

@@ -50,7 +50,9 @@
 #ifndef blkdev
 # define blkdev(x,m,maj,min) mknod((x), S_IFBLK|(m), makedev((maj),(min)))
 #endif
-
+#ifndef S_ISEXEC
+# define S_ISEXEC(m) (((m) & S_IXUSR) == S_IXUSR)
+#endif
 #ifndef UNUSED
 #define UNUSED(x) UNUSED_ ## x __attribute__ ((unused))
 #endif
@@ -87,7 +89,7 @@ void    set_hostname    (char *hostname);
 int     run             (char *cmd);
 int     run_interactive (char *cmd, char *fmt, ...);
 pid_t   run_getty       (char *cmd, char *argv[]);
-int	run_parts	(char *dir, ...);
+int	run_parts	(char *dir, char *cmd);
 
 /* strlcpy.c */
 size_t strlcpy(char *dst, const char *src, size_t siz);