bug#457: wdired and auto-revert-mode

[martin rudalics <rudalics@gmx.at>]

 >  > The buffer-modified flag is mostly good enough for buffers visiting
 >  > ordinary files, but is hard to keep correct for fancy buffers like
 >  > Dired buffers.  Of course, this wasn't so important before
 >  > auto-revert-mode existed.
 >
 > Yes. And this is also the reason for another, much worse bug which
 > makes auto-revert-mode in dired nearly useless:
 >
 > If you copy files etc. (what else should you do with dired?), your
 > buffer gets buffer-modified-p, which means that auto-reverting doesn't
 > take place any more until you revert manually with g.

The buffer-modified status of dired-buffers has no significance: Do
`dired-mark' for some file and undo that via `dired-unmark' or plain
`undo'.  The buffer will remain to appear modified.  Do `dired-unmark'
for some file in a fresh dired buffer.  The buffer will appear modified.
We'd have to specify the semantics of modifiedness for dired buffers
first.  Then we could decide what to do when a directory is modified by
external intervention and autorevert picks up those changes.

OTOH wdired DTRT WRT `undo' and we probably shouldn't let autorevert
interfere with this.

martin