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/gnulib-cache.m4

@@ -0,0 +1,41 @@
+# Copyright (C) 2002-2010 Free Software Foundation, Inc.
+#
+# This file is free software, distributed under the terms of the GNU
+# General Public License.  As a special exception to the GNU General
+# Public License, this file may be distributed as part of a program
+# that contains a configuration script generated by Autoconf, under
+# the same distribution terms as the rest of that program.
+#
+# Generated by gnulib-tool.
+#
+# This file represents the specification of how gnulib-tool is used.
+# It acts as a cache: It is written and read by gnulib-tool.
+# In projects that use version control, this file is meant to be put under
+# version control, like the configure.ac and various Makefile.am files.
+
+
+# Specification in the form of a command-line invocation:
+#   gnulib-tool --import --dir=. --lib=libgnu --source-base=grub-core/gnulib --m4-base=m4 --doc-base=doc --tests-base=tests --aux-dir=build-aux --no-libtool --macro-prefix=gl --no-vc-files argp error fnmatch getdelim getline progname regex
+
+# Specification in the form of a few gnulib-tool.m4 macro invocations:
+gl_LOCAL_DIR([])
+gl_MODULES([
+  argp
+  error
+  fnmatch
+  getdelim
+  getline
+  progname
+  regex
+])
+gl_AVOID([])
+gl_SOURCE_BASE([grub-core/gnulib])
+gl_M4_BASE([m4])
+gl_PO_BASE([])
+gl_DOC_BASE([doc])
+gl_TESTS_BASE([tests])
+gl_LIB([libgnu])
+gl_MAKEFILE_NAME([])
+gl_MACRO_PREFIX([gl])
+gl_PO_DOMAIN([])
+gl_VC_FILES([false])