bug#11772: 24.1; A click changes the primary selection

[Vincent Lefevre <vincent@vinc17.net>]

If there is something selected in the Emacs window but is no longer
the PRIMARY selection and one clicks somewhere in the window, the
primary selection is changed to what had been selected.

To reproduce the bug:

1. Run "emacs -Q" under X.
2. Select something in the Emacs window, e.g. "This buffer".
3. Select something in some other application that supports the
   PRIMARY selection, e.g. xterm.
4. Optional: paste the PRIMARY selection somewhere (but not in the
   Emacs window opened above). As expected, one can see that the
   selection done in (3) is pasted.
5. Click somethere in the Emacs window, with the left button.
   As expected, the selection is no longer highlighted.
6. Paste the PRIMARY selection somewhere: it is the one from Emacs
   (e.g. "This buffer"), i.e. in (2), that is pasted instead of the
   most recent PRIMARY selection from (3).

This is a regression: GNU Emacs 23.4.1 from Debian doesn't have this
problem.


In GNU Emacs 24.1.1 (x86_64-unknown-linux-gnu, GTK+ Version 2.24.10)
 of 2012-06-19 on xvii
Windowing system distributor `The X.Org Foundation', version 11.0.11201902
Configured using:
 `configure '--prefix=/usr/local/emacs-24.1' '--enable-asserts''

Important settings:
  value of $LC_ALL: nil
  value of $LC_COLLATE: POSIX
  value of $LC_CTYPE: en_US.UTF-8
  value of $LC_MESSAGES: nil
  value of $LC_MONETARY: nil
  value of $LC_NUMERIC: nil
  value of $LC_TIME: en_DK
  value of $LANG: POSIX
  value of $XMODIFIERS: nil
  locale-coding-system: utf-8-unix
  default enable-multibyte-characters: t

Major mode: Lisp Interaction

Minor modes in effect:
  display-time-mode: t
  show-paren-mode: t
  tooltip-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
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  column-number-mode: t
  line-number-mode: t
  transient-mark-mode: t

Recent input:
<escape> x r e p o r t b u <tab> <backspace> <backspace> 
<tab> <return>

Recent messages:
Loading /home/vinc17/share/emacs/site-lisp/mutteditor.el (source)...done
Loading time...done
For information about GNU Emacs and the GNU system, type C-h C-a.

Load-path shadows:
~/share/emacs/site-lisp/sh-script hides /usr/local/emacs-24.1/share/emacs/24.1/lisp/progmodes/sh-script

Features:
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ietf-drums mm-util mail-prsvr mail-utils time cus-start cus-load paren
cc-styles cc-align cc-engine cc-vars cc-defs regexp-opt time-date
tooltip ediff-hook vc-hooks lisp-float-type mwheel x-win x-dnd tool-bar
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