bug#11655: 24.1; Customize: clicking down-pointing triangle should not raise error

[Drew Adams]

emacs -Q
 
M-x customize-group custom-buffer
 
Click the right-pointing triangle for Custom Buffer Style, to show the
details.
 
Choose the brackets choice (click).
 
State > Set for current session.
 
Click the down-pointing triangle.
 
That raises an error.  It should not.  You should be able to open and
close (show & hide the details) of any customize items.  This is
important because hiding them helps you see others.
 
We should not confuse showing an informative message with raising an
error.  If you want to draw user attention, the do so: flash something,
ring a bell,... whatever.
 
But do NOT prevent the user from doing what s?he tries to do: hide the
entry.  That makes no sense and is user unfriendly.  Hiding details is
not an error.
 

In GNU Emacs 24.1.1 (i386-mingw-nt5.1.2600)
 of 2012-06-01 on MARVIN
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'