bug#3687: 23.1.50; inconsistency in multibyte eight-bit regexps

The following results look inconsistent:

  (string-match (string-to-multibyte "\x80") (string-to-multibyte "\x80"))
  => 0
  (string-match (string-to-multibyte "\x80") "\x80")
  => nil

  (string-match (string-to-multibyte "[\x80]") (string-to-multibyte "\x80"))
  => nil
  (string-match (string-to-multibyte "[\x80]") "\x80")
  => 0

				     YAMAMOTO Mitsuharu
				[email protected]

In GNU Emacs 23.1.50.1 (sparc-sun-solaris2.8, X toolkit, Xaw3d scroll bars)
 of 2009-06-26 on church
Windowing system distributor `The X.Org Foundation', version 11.0.10402000
configured using `configure  'LDFLAGS=-L/usr/local/lib -R/usr/local/lib' 'CPPFLAGS=-I/usr/local/lib''

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: ja
  value of $XMODIFIERS: nil
  locale-coding-system: japanese-iso-8bit-unix
  default-enable-multibyte-characters: t

Major mode: Fundamental

Minor modes in effect:
  tooltip-mode: t
  tool-bar-mode: t
  mouse-wheel-mode: t
  menu-bar-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  blink-cursor-mode: t
  global-auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  line-number-mode: t
  transient-mark-mode: t