bug#30823: 25.3; modification-hooks of overlays are not run in some cases

[Stefan Monnier]

>> Coming back to this, there is also the possibility of passing true for
>> PREPARE, though I'm not sure if that would be better or worse.  Any
>> comments?
> AFAIR, we never want to use PREPARE = true when dealing with the
> *Messages* buffer, you can see that elsewhere in message_dolog.  The
> reason I believe is that we might trigger infinite recursion if the
> modification hooks log a message for some reason.

The current code already allows running `message` in this way (and that
leads to suboptimal behavior, tho nothing really serious).  I think we
should use `true` here and then actively try and detect nested uses of
`message` and deal with those in an ad-hoc way (e.g. bind
inhibit-modification-hooks during the nested call so the recursion is at
most 2 deep).

The benefit is that it makes this part of the code more "normal" and
will probably fix/avoid other bugs like this one.

The patch I sent in
https://lists.gnu.org/archive/html/emacs-devel/2018-05/msg00600.html
went in this direction and my experimentation with it did not encounter
any serious problem.  IOW I think the comment near message_dolog is
largely out of date.


        Stefan