bug#11738: 24.1.50; Regression: `modify-frame-parameters' is broken for `left' & `top'

[Drew Adams]

Note: It still works fine in the release (24.1), but is broken in this
build.
 
emacs -Q
 
In *scratch*:
 
(setq new (- (frame-parameter nil 'left) 10))
(setq new `(left + ,new))
(modify-frame-parameters nil (list new))
 
IOW, try to set `left' or `top' to a value that is a cons whose car is
`left' or `top', whose cadr is `+' or `-', and whose caddr is some new
value.  Nothing happens.

This is a regression wrt ALL previous Emacs versions (well, ever
since we had frames).  It is important that the cons form of these
parameter values continue to be accepted, as it has always been.

See also this, which brought the bug to my attention:
http://lists.gnu.org/archive/html/help-gnu-emacs/2012-06/msg00227.html


In GNU Emacs 24.1.50.1 (i386-mingw-nt5.1.2600)
 of 2012-06-18 on MARVIN
Bzr revision: 108646 michael.albinus@gmx.de-20120617185439-jfcgwwbr97nbflkz
Windowing system distributor `Microsoft Corp.', version 5.1.2600
Configured using:
 `configure --with-gcc (4.6) --no-opt --enable-checking --cflags
 -ID:/devel/emacs/libs/libXpm-3.5.8/include
 -ID:/devel/emacs/libs/libXpm-3.5.8/src
 -ID:/devel/emacs/libs/libpng-dev_1.4.3-1/include
 -ID:/devel/emacs/libs/zlib-dev_1.2.5-2/include
 -ID:/devel/emacs/libs/giflib-4.1.4-1/include
 -ID:/devel/emacs/libs/jpeg-6b-4/include
 -ID:/devel/emacs/libs/tiff-3.8.2-1/include
 -ID:/devel/emacs/libs/gnutls-3.0.9/include
 -ID:/devel/emacs/libs/libiconv-1.13.1-1-dev/include
 -ID:/devel/emacs/libs/libxml2-2.7.8/include/libxml2'