(locale-preferred-coding-systems): Add "jpn".

lisp/international/mule-cmds.el

@@ -1916,6 +1916,7 @@ the language name that would otherwise be used for this locale.")
      ("ja.*[._]jis7" . iso-2022-jp)
      ("ja.*[._]pck" . japanese-shift-jis)
      ("ja.*[._]sjis" . japanese-shift-jis)
+     ("jpn" . japanese-shift-jis)   ; MS-Windows uses this.
      (".*[._]utf" . utf-8)))
   "List of pairs of locale regexps and preferred coding systems.
 The first element whose locale regexp matches the start of a downcased locale