bug#3181: 23.0.92; Windows: text-scale-decrease changes font family, not just font size

[Eric Hanchrow <eric.hanchrow@gmail.com>]

I started Emacs with -Q.

I noted with pleasure that the displayed font was Courier, which I
like because it's monospaced.

I shift-left-clicked in the middle of the screen, and chose "decrease
buffer text size" from the menu that appeared.

I noticed that the font was now .. I dunno ... Ariel, I guess;
whatever it is, it ain't Courier and it ain't monospaced.  (It was,
however, smaller than what I'd started with, so that's something.)

For what it's worth, no similar problem happens on *nix, with an emacs as of

    Author: Chong Yidong <cyd@stupidchicken.com>
    Date:   Tue Mar 24 17:37:58 2009 +0000

	(Ffloat_time): Doc fix (Bug#2768).

Instead, Emacs initially starts with (what appears to be) Bitstream
Vera Sans Mono, and when I reduce its size, it's still the same font,
just smaller.

If Emacs crashed, and you have the Emacs process in the gdb debugger,
please include the output from the following gdb commands:
    `bt full' and `xbacktrace'.
If you would like to further debug the crash, please read the file
c:/cygwin/usr/local/src/emacs/etc/DEBUG for instructions.


In GNU Emacs 23.0.92.1 (i386-mingw-nt6.0.6001)
 of 2009-04-13 on ERICH-DEV
Windowing system distributor `Microsoft Corp.', version 6.0.6001
configured using `configure --with-gcc (3.4)'

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: ENU
  value of $XMODIFIERS: nil
  locale-coding-system: cp1252
  default-enable-multibyte-characters: t

Major mode: Lisp Interaction

Minor modes in effect:
  text-scale-mode: t
  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
  font-lock-mode: t
  blink-cursor-mode: t
  global-auto-composition-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  line-number-mode: t
  transient-mark-mode: t

Recent input:
C-- C-- C-- C-h c C-- C-h w t e x t - s c <tab> d <tab>
<return> <help-echo> <S-down-mouse-1> <S-down-mouse-1>
C-h c C-0 <S-down-mouse-1> M-x m e n u - s e <tab>
<return> <S-down-mouse-1> M-x r e [ p <backspace> <backspace>
p o r t - e m <tab> <return>

Recent messages:
For information about GNU Emacs and the GNU system, type C-h C-a.
C-- runs the command negative-argument
text-scale-decrease is not on any key
C-0 runs the command digit-argument