bug#12726: 24.2.50; `imenu' should pass NOMSG to `push-mark'

[Drew Adams]

The call (push-mark) in command `imenu' should be
(push-mark nil 'NOMSG).
 
Menu items can include so-called "special" menu items, which are in
effect function calls.  The function called could do most anything,
including ignore the POSITION entry for the menu item and including
display a message.  It is not appropriate, at least in these cases (and
I think in all cases) for `push-mark' to display the message "Mark set".

In GNU Emacs 24.2.50.1 (i386-mingw-nt5.1.2600)
 of 2012-10-22 on DANI-PC
Bzr revision: 110618 monnier@iro.umontreal.ca-20121022132928-232zm0fecassmhfb
Windowing system distributor `Microsoft Corp.', version 5.1.2600
Configured using:
 `configure --with-gcc (4.7) --no-opt --enable-checking --cflags
 -I../../libs/libxpm-3.5.8/include -I../../libs/libxpm-3.5.8/src
 -I../../libs/libpng-1.4.10 -I../../libs/zlib-1.2.6
 -I../../libs/giflib-4.1.4-1/include -I../../libs/jpeg-6b-4/include
 -I../../libs/tiff-3.8.2-1/include
 -I../../libs/libxml2-2.7.8-w32-bin/include/libxml2
 -I../../libs/gnutls-3.0.16/include
 -I../../libs/libiconv-1.14-2-mingw32-dev/include'