Re: charset="Windows-31J"

Hi,

NAKAJI Hiroyuki reported that some Japanese mails use the
`Windows-31J' charset which Emacs doesn't know.  According to
the web pages, etc.[1], it can be treated as `cp932' and
NAKAJI-san contributed a tiny patch to map `windows-31j' to
`cp932' in `mm-charset-synonym-alist'.  I've applied it in both
the trunk and the v5-10 branch.  Thanks NAKAJI-san.

[1]
> http://ja.wikipedia.org/wiki/Microsoft%E6%BC%A2%E5%AD%97%E3%82%B3%E3%83%BC%E3%83%89
> http://www2d.biglobe.ne.jp/~msyk/charcode/cp932/index.html

> Microsoft also mentioned in KB260818 as follows:

> Also note that the following aliases in builds later than the
> 3200 series will be mapped to the MS932 encoding rather than
> "SJIS".

>    "shift_jis"       --> "MS932"
>    "ms_kanji"        --> "MS932"
>    "csshiftjis"      --> "MS932"
>    "windows-31j"     --> "MS932"
>    "cswindows31j"    --> "MS932"