detect-coding-string doesn't return all possibilities

[Jesper Harder]

`detect-coding-string' doesn't return all possible coding systems for a
string.  For example:

(detect-coding-string (encode-coding-string "안녕" 'korean-iso-8bit))
=> (iso-latin-1 iso-latin-1 raw-text chinese-big5 no-conversion)

Clearly korean-iso-8bit is a possible coding system, but this is not
detected.

The same bug happens in CVS Emacs.


In GNU Emacs 21.2.1 (i386-redhat-linux-gnu, X toolkit, Xaw3d scroll bars)
 of 2002-04-09 on porky.devel.redhat.com
configured using `configure  i386-redhat-linux --prefix=/usr --exec-prefix=/usr 
--bindir=/usr/bin --sbindir=/usr/sbin --sysconfdir=/etc --datadir=/usr/share 
--includedir=/usr/include --libdir=/usr/lib --libexecdir=/usr/libexec 
--localstatedir=/var --sharedstatedir=/usr/com --mandir=/usr/share/man 
--infodir=/usr/share/info --with-gcc --with-pop --with-sound'
Important settings:
  value of $LC_ALL: nil
  value of $LC_COLLATE: nil
  value of $LC_CTYPE: nil
  value of $LC_MESSAGES: nil
  value of $LC_MONETARY: nil
  value of $LC_NUMERIC: nil
  value of $LC_TIME: nil
  value of $LANG: en_US.iso88591
  locale-coding-system: iso-latin-1
  default-enable-multibyte-characters: t