bug#23444: 25.0.92; activate-mark-hook does not run after a command has changed the region

[Nicolas Richard <youngfrog@members.fsf.org>]

activate-mark-hook contains the following in its docstring:

> It is also run at the end of a command, if the mark is active and
> it is possible that the region may have changed.

However, when changing the region, nothing happens. As an example I
tried evaluating:

(defun foo ()
  (message "ran: %s" this-command))
(add-hook 'activate-mark-hook 'foo)

then using C-M-SPC (mark-sexp) correctly showed "ran: mark-sexp", but
moving the cursor afterwards doesn't produce any more message.

FWIW this was mentionned in bug#902 (and then promptly forgotten, due to
the main topic being something else in that report).

(side note : in the git repo these docstrings were introduced in commit
0251bafb90e63cc7f428e1b91db436c32ad2677c authored by Richard Stallman.
In the lisp/ChangeLog.12 the author of those lines is said to be Chong
Yidong. I guess I will pretend I did not see this.)

In GNU Emacs 25.0.92.1 (i686-pc-linux-gnu, X toolkit, Xaw3d scroll bars)
 of 2016-03-04 built on localhost
Repository revision: 620951fe22a6ecc2edc1f78d961f52566a7fe2b6
Windowing system distributor 'The X.Org Foundation', version 11.0.11604000
System Description:	Gentoo Base System release 2.2

Configured using:
 'configure --with-x-toolkit=lucid 'CFLAGS= ''

-- 
Nicolas Richard