Add a --locale-directory option to grub-install and related tools.

* include/grub/util/install.h (GRUB_INSTALL_OPTIONS): Add
--locale-directory option.
(enum grub_install_options): Add
GRUB_INSTALL_OPTIONS_LOCALE_DIRECTORY.
* util/grub-install-common.c (grub_install_help_filter): Handle
GRUB_INSTALL_OPTIONS_LOCALE_DIRECTORY.
(grub_install_parse): Likewise.
(get_localedir): New function to check for a user-provided option
before trying grub_util_get_localedir.
(copy_locales): Use get_localedir rather than
grub_util_get_localedir.  Handle differing locale directory layouts.
(grub_install_copy_files): Likewise.

include/grub/util/install.h

@@ -47,6 +47,9 @@
   { "override-directory", GRUB_INSTALL_OPTIONS_DIRECTORY2,		\
       N_("DIR"), OPTION_HIDDEN,						\
     N_("use images and modules under DIR [default=%s/<platform>]"), 1 },  \
+  { "locale-directory", GRUB_INSTALL_OPTIONS_LOCALE_DIRECTORY,		\
+      N_("DIR"), 0,							\
+    N_("use translations under DIR [default=%s]"), 1 },			\
   { "grub-mkimage", GRUB_INSTALL_OPTIONS_GRUB_MKIMAGE,		\
       "FILE", OPTION_HIDDEN, 0, 1 },					\
     /* TRANSLATORS: "embed" is a verb (command description).  "*/	\
@@ -102,6 +105,7 @@ enum grub_install_options {
   GRUB_INSTALL_OPTIONS_INSTALL_LOCALES,
   GRUB_INSTALL_OPTIONS_INSTALL_COMPRESS,
   GRUB_INSTALL_OPTIONS_DIRECTORY2,
+  GRUB_INSTALL_OPTIONS_LOCALE_DIRECTORY,
   GRUB_INSTALL_OPTIONS_GRUB_MKIMAGE
 };