Log Message:
Update converters/nkf to 2.05.

1. Added --guess option which print guessed character encoding.
2. Added --cp932inv options which enable to make some characters
   conversion compatible with Code Page 932 (CP932) when converting
   to Shift_JIS.
3. Added --prefix option.  When converting to Shift_JIS, second byte of
   converted character may be "meta" character.  --prefix option allow
   escape these characters.
4. Added support for JIS X 0212.