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/nl_langinfo.m4

@@ -0,0 +1,25 @@
+# nl_langinfo.m4 serial 3
+dnl Copyright (C) 2009, 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_FUNC_NL_LANGINFO],
+[
+  AC_REQUIRE([gl_LANGINFO_H_DEFAULTS])
+  AC_REQUIRE([gl_LANGINFO_H])
+  AC_CHECK_FUNCS_ONCE([nl_langinfo])
+  if test $ac_cv_func_nl_langinfo = yes; then
+    if test $HAVE_LANGINFO_CODESET = 1 && test $HAVE_LANGINFO_ERA = 1; then
+      :
+    else
+      REPLACE_NL_LANGINFO=1
+      AC_DEFINE([REPLACE_NL_LANGINFO], [1],
+        [Define if nl_langinfo exists but is overridden by gnulib.])
+      AC_LIBOBJ([nl_langinfo])
+    fi
+  else
+    HAVE_NL_LANGINFO=0
+    AC_LIBOBJ([nl_langinfo])
+  fi
+])