Use gnulib-tool to create gnulib source files.

* Add gnulib files generated by gnulib-tool in build-aux, m4 and
    grub-core/gnulib directories
    * .bzignore: Add **/.deps and autogenerated gnulib files
    * configure.ac: Assign auxiliary directory to build-aux, add invocation
    of gnulib macros, add grub-core/gnulib/Makefile
    * Makefile.am: Add gnulib directory in SUBDIRS (removing unnecessary .),
    include m4 directory to aclocal.
    * Makefile.util.def: Remove direct compilation of gnulib source files
    and use the new grub-core/gnulib/libgnu.a.
    * build-aux/config.rpath: move config.rpath from top directory to
    build-aux
    * conf/Makefile.common: Remove the macro _GL_UNUSED already defined
    in gnulib headers
    * conf/Makefile.extra-dist: Add m4/gnulib-cache.m4
    * grub-core/Makefile.core.def: Remove unnecessary extra_dist
    * grub-core/lib/posix_wrap/localcharset.h (locale_charset): Update
    header.
    * grub-core/lib/posix_wrap/langinfo.h (nl_langinfo): Return static
    string.

m4/double-slash-root.m4

@@ -0,0 +1,38 @@
+# double-slash-root.m4 serial 4   -*- Autoconf -*-
+dnl Copyright (C) 2006, 2008-2010 Free Software Foundation, Inc.
+dnl This file is free software; the Free Software Foundation
+dnl gives unlimited permission to copy and/or distribute it,
+dnl with or without modifications, as long as this notice is preserved.
+
+AC_DEFUN([gl_DOUBLE_SLASH_ROOT],
+[
+  AC_REQUIRE([AC_CANONICAL_HOST])
+  AC_CACHE_CHECK([whether // is distinct from /], [gl_cv_double_slash_root],
+    [ if test x"$cross_compiling" = xyes ; then
+        # When cross-compiling, there is no way to tell whether // is special
+        # short of a list of hosts.  However, the only known hosts to date
+        # that have a distinct // are Apollo DomainOS (too old to port to),
+        # Cygwin, and z/OS.  If anyone knows of another system for which // has
+        # special semantics and is distinct from /, please report it to
+        # <bug-gnulib@gnu.org>.
+        case $host in
+          *-cygwin | i370-ibm-openedition)
+            gl_cv_double_slash_root=yes ;;
+          *)
+            # Be optimistic and assume that / and // are the same when we
+            # don't know.
+            gl_cv_double_slash_root='unknown, assuming no' ;;
+        esac
+      else
+        set x `ls -di / // 2>/dev/null`
+        if test "$[2]" = "$[4]" && wc //dev/null >/dev/null 2>&1; then
+          gl_cv_double_slash_root=no
+        else
+          gl_cv_double_slash_root=yes
+        fi
+      fi])
+  if test "$gl_cv_double_slash_root" = yes; then
+    AC_DEFINE([DOUBLE_SLASH_IS_DISTINCT_ROOT], [1],
+      [Define to 1 if // is a file system root distinct from /.])
+  fi
+])