bug#50431: revert-buffer doesn't preserve read-onlyness

[Juri Linkov <juri@linkov.net>]

>> >> but reverting loses view-mode:
>> >>
>> >>   C-h C-t  -- note "View" on the mode-line;
>> >>   C-x x g  -- "View" is lost.
>> >
>> > Hm, yes.  Reverting a buffer disables all the minor modes?
>>
>> Maybe minor modes should be restored after reverting?
>
> Only the minor modes that are automatically turned on when visiting
> the file.  Reverting should produce the same effect as killing the
> buffer and then visiting the file anew, nothing more, nothing less.

In the above example, `C-h C-t' `C-x x g' doesn't preserve the same state
as visiting the file anew with `C-h C-t'.

> For that reason, I'm not sure the change that preserves the read-only
> status across reverts is correct.  At the very least, it should be an
> opt-in feature, IMO.

It was a regression when reverting stopped to preserve the read-only status
that worked in older versions.  OTOH, in older versions reverting didn't
preserve the minor modes.