bug#18828: 24.4; Early collision warning when 'create-lockfiles' is set to nil

[Dani Moncayo <dmoncayo@gmail.com>]

Recipe:
0. emacs -Q
1. Eval: (setq create-lockfiles nil)
2. Visit some file
3. With another program, update the visited file.
4. Try to make some change to the buffer.

------------

Without step 1, Emacs does TRT, i.e., it detects that I'm trying to
make the first change to a buffer whose file has already changed since
it was visited, so it warns me with:

 foo changed on disk; really edit the buffer? (y, n, r or C-h)

But with step 1, Emacs doesn't warn me until I try to save the buffer;
then it shows me this:

  foo has changed since visited or saved.  Save anyway? (yes or no)

(BTW: the above message does not get archived in the *Messages*
buffer.  Why not?  I think it should, as with the first warning)

Well, I think that Emacs should warn me on step 4, regardles of
whether I did step 1 or not.

I set `create-lockfiles' to nil in my init file because I don't want
Emacs to create temporary files of any kind, but obviously I want to
be warned whenever I am about to change a buffer whose file has
changed on disk after it was last read by Emacs.

I observe this bug both with the last 24.4 release and with the trunk.

In GNU Emacs 24.4.1 (i686-pc-mingw32)
 of 2014-10-20 on LEG570
Windowing system distributor `Microsoft Corp.', version 6.3.9600
Important settings:
  value of $LANG: ENU
  locale-coding-system: cp1252

-- 
Dani Moncayo