Wrong mime-charset for chinese gb2312 coding system

[Zhang Wei]

According to:

http://www.isi.edu/in-notes/iana/assignments/character-sets

"cn-gb" is not an official registration.

The prefered mime-charset is "gb2312", not "cn-gb". 
Some popular mail client such as "Mozilla-thunderbird"
or "Emacs Mew" don't recognize "cn-gb" charset, 
and the messages don't display properly.

This bug had been fixed in the main branch, but was 
somehow reintroduced in the emacs-unicode-2 branch.
----------------------------------------------------------------
*** chinese.el  2004-10-04 20:09:55.000000000 +0800
--- chinese.el.new      2005-06-04 02:45:48.642246024 +0800
***************
*** 75,86 ****
  ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
  
  (define-coding-system 'chinese-iso-8bit
!   "ISO 2022 based EUC encoding for Chinese GB2312 (MIME:CN-GB)."
    :coding-type 'iso-2022
    :mnemonic ?c
    :charset-list '(ascii chinese-gb2312)
    :designation [ascii chinese-gb2312 nil nil]
!   :mime-charset 'cn-gb)
  
  (define-coding-system-alias 'cn-gb-2312 'chinese-iso-8bit)
  (define-coding-system-alias 'euc-china 'chinese-iso-8bit)
--- 75,86 ----
  ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
  
  (define-coding-system 'chinese-iso-8bit
!   "ISO 2022 based EUC encoding for Chinese GB2312 (MIME:GB2312)."
    :coding-type 'iso-2022
    :mnemonic ?c
    :charset-list '(ascii chinese-gb2312)
    :designation [ascii chinese-gb2312 nil nil]
!   :mime-charset 'gb2312)
  
  (define-coding-system-alias 'cn-gb-2312 'chinese-iso-8bit)
  (define-coding-system-alias 'euc-china 'chinese-iso-8bit)
--------------------------------------------------------------

In GNU Emacs 23.0.0.1 (i686-pc-linux-gnu, GTK+ Version 2.6.4)
 of 2005-05-30 on dorm
Distributor `The XFree86 Project, Inc', version 11.0.40300001
configured using `configure 'CFLAGS=-g' 'prefix=/usr' '--with-x-toolkit=gtk''