autoconf-mode: comment-dwim behaviour

[Kevin Ryde]

In GNU Emacs 21.1.1 (i386-debian-linux-gnu, X toolkit)
 of 2001-10-22 on raven, modified by Debian
configured using `configure  i386-debian-linux-gnu --prefix=/usr 
--sharedstatedir=/var/lib --libexecdir=/usr/lib --localstatedir=/var/lib 
--infodir=/usr/share/info --mandir=/usr/share/man --with-pop=yes --with-x=yes 
--with-x-toolkit=yes'
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: C
  locale-coding-system: nil
  default-enable-multibyte-characters: t


Running up "emacs -q -no-site-file configure.in" on an non-existant
configure.in and pressing M-; twice produces

        dnl                     dnl 

whereas I would have hoped that the second M-; would just leave point
positioned after the first dnl.

Further M-; presses insert extra spaces after the second dnl, which
seems unhelpful too.

Those extra spaces can also be seen by pressing M-; on a line like,

AC_FOO                dnl  a comment

point gets positioned before the "a", but an extra space inserted each
time M-; is pressed.