libcgroup-internal.h: reorder the header stacking.

`man 3 fts` not only specifies the headers to be included, but
also the order.  <fts.h> must be included after <sys/types.h>
and <sys/stats.h>.  On glibc and uClibc systems, an incorrect
order does not pose a problem, but on musl this leads to undefine
types such as dev_t and friends.

Signed-off-by: Anthony G. Basile <blueness@gentoo.org>

diff -Naur libcgroup-0.41.orig/src/libcgroup-internal.h libcgroup-0.41/src/libcgroup-internal.h
--- libcgroup-0.41.orig/src/libcgroup-internal.h	2015-07-13 21:08:26.740965713 -0400
+++ libcgroup-0.41/src/libcgroup-internal.h	2015-07-13 21:09:40.774962164 -0400
@@ -21,12 +21,12 @@
 #endif
 
 #include "config.h"
-#include <fts.h>
 #include <libcgroup.h>
 #include <limits.h>
 #include <pthread.h>
-#include <sys/stat.h>
 #include <sys/types.h>
+#include <sys/stat.h>
+#include <fts.h>
 #include <setjmp.h>
 
 /* Maximum number of mount points/controllers */