completing-read doesn't require exact match when completion-ignore-case is set

[Urban Engberg]

   Please describe exactly what actions triggered the bug
   and the precise symptoms of the bug:

Type:

   M-: (setq completion-ignore-case t)
   M-: (completing-read "Eh? " (list "fooA" "fooB") nil t)

and answer "fooa" at the prompt.  completing-read the returns
"fooa", even though REQUIRE-MATCH is set to t.

It could be argued that this should be the expected behaviour (as
completion-ignore-case is set to t).  However, it has some not so
nice effects on a number of interactive commands, as e.g. those
using a read-buffer with require-match set:

   M-: (read-buffer "Buffer: " nil t)

This ought evaluate to the name an existing buffer name.  But if
completion-ignore-case is set, the above mentioned fact about
completing-read makes it possible to return any of

   foo Foo fOo

etc., if there exists a buffer named "foo".  We thus get the name of a
non-existing buffer, which clearly should not be possible.


   In GNU Emacs 21.3.50.2 (i686-pc-linux-gnu, X toolkit, Xaw3d scroll bars)
    of 2004-08-13 on uelinux
   configured using `configure  'CFLAGS=-g -v''

   Important settings:
     value of $LC_ALL: en_US.iso885915
     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.UTF-8
     locale-coding-system: iso-latin-9
     default-enable-multibyte-characters: t

   Major mode: Group

   Minor modes in effect:
     gnus-topic-mode: t
     gnus-undo-mode: t
     auto-image-file-mode: t
     auto-compression-mode: t
     mouse-wheel-mode: t
     menu-bar-mode: t
     global-font-lock-mode: t
     font-lock-mode: t
     unify-8859-on-encoding-mode: t
     utf-translate-cjk-mode: t
     temp-buffer-resize-mode: t
     column-number-mode: t
     line-number-mode: t

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