Update Gnulib to v0.0-6827-g39c3009; use the `dirfd' module.

* m4/gnulib-cache.m4: Use `dirfd'.

* libguile/filesys.c: Include Gnulib's <dirent.h> directly.
  (dirfd): Remove.  Suggested by Bruno Haible <bruno@clisp.org>.

lib/dirfd.c

@@ -0,0 +1,32 @@
+/* dirfd.c -- return the file descriptor associated with an open DIR*
+
+   Copyright (C) 2001, 2006, 2008-2012 Free Software Foundation, Inc.
+
+   This program is free software: you can redistribute it and/or modify
+   it under the terms of the GNU Lesser General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+/* Written by Jim Meyering. */
+
+#include <config.h>
+
+#include <dirent.h>
+#include <errno.h>
+
+int
+dirfd (DIR *dir_p)
+{
+  int fd = DIR_TO_FD (dir_p);
+  if (fd == -1)
+    errno = ENOTSUP;
+  return fd;
+}