bug#29846: scroll and fontify takes longer time for file in slow network

[Eli Zaretskii]

> From: Stefan Monnier <monnier@IRO.UMontreal.CA>
> Date: Wed, 27 Dec 2017 15:49:56 -0500
> Cc: 29846@debbugs.gnu.org
> 
> > I have remote drive (//server/path) mapped to my windows system (samba?).
> > The network is slow, and it takes some time to open the file. However,
> > after I have the file opened and scroll down, it takes a long time to
> > scroll to the next screen. It gets worse if the jit-lock-debug-mode is on.
> > After that if I try to scroll back to those has been fontified, it get
> > fluent as expected.
> 
> I believe this bug was introduced by yours truly
> in commit 6bc76cee212aab0a2c02f8c28213fc842cc7880f:
> 
>   Author: Stefan Monnier <monnier@iro.umontreal.ca>
>   Date:   Tue Apr 8 21:48:07 2014 -0400
> 
>     * src/insdel.c (prepare_to_modify_buffer_1): Cancel lock-file checks and
>     region handling (and don't call signal_before_change) if
>     inhibit_modification_hooks is set.
>     (signal_before_change): Don't check inhibit_modification_hooks any more.
>     * lisp/subr.el (with-silent-modifications): Don't bind deactivate-mark,
>     buffer-file-name, and buffer-file-truename any more.
> 
> And I think the patch below hence belongs in emacs-26.  Any objection?

LGTM, please push to emacs-26.

Thanks.