Add const keyword to grub_env_get and gettextize week days.

* grub-core/hook/datehook.c (grub_datetime_names): Make const.
	(grub_read_hook_datetime): Return const char *.
	* grub-core/kern/env.c (grub_env_get): Return const char *. All users
	updated.
	* grub-core/normal/datetime.c (grub_weekday_names): Make const.
	Mark for gettext.
	(grub_get_weekday_name): Return const char *. Call gettext.
	* grub-core/script/argv.c (grub_script_argv_append): Receive const
	char * and len as the argument. All users updated.
	(grub_script_argv_split_append): Receive const char *.
	* include/grub/datetime.h (grub_get_weekday_name): Update proto.
	* include/grub/env.h (grub_env_get): Likewise.
	(grub_env_read_hook_t): Return const char *.
	* include/grub/script_sh.h (grub_script_argv_append): Update proto.
	(grub_script_argv_split_append): Likewise.

grub-core/commands/i386/pc/drivemap.c

@@ -363,7 +363,7 @@ uninstall_int13_handler (void)
 static int
 grub_get_root_biosnumber_drivemap (void)
 {
-  char *biosnum;
+  const char *biosnum;
   int ret = -1;
   grub_device_t dev;
 

grub-core/commands/legacycfg.c

@@ -344,7 +344,7 @@ grub_cmd_legacy_kernel (struct grub_command *mycmd __attribute__ ((unused)),
 	int bsd_part = -1;
 	{
 	  grub_device_t dev;
-	  char *hdbiasstr;
+	  const char *hdbiasstr;
 	  int hdbias = 0;
 	  hdbiasstr = grub_env_get ("legacy_hdbias");
 	  if (hdbiasstr)

grub-core/commands/loadenv.c

@@ -43,7 +43,7 @@ open_envblk_file (char *filename)
 
   if (! filename)
     {
-      char *prefix;
+      const char *prefix;
 
       prefix = grub_env_get ("prefix");
       if (prefix)
@@ -346,7 +346,7 @@ grub_cmd_save_env (grub_extcmd_context_t ctxt, int argc, char **args)
 
   while (argc)
     {
-      char *value;
+      const char *value;
 
       value = grub_env_get (args[0]);
       if (value)

grub-core/commands/wildcard.c

@@ -436,7 +436,7 @@ wildcard_expand (const char *s, char ***strs)
 
 	  else if (*start == '/') /* no device part */
 	    {
-	      char *root;
+	      const char *root;
 	      char *prefix;
 
 	      root = grub_env_get ("root");