bug#3973: cleanup view-mode usage in vc-resynch-window

>> > I have removed that code locally for a while and didn't see any
>> > problem.  But I don't explicitly use view-mode, so...
>> 
>> Obiously the code only makes a difference when you use view-read-only,
>> so you'll need to set it to a non-nil value before doing any test.

> [I've never done anything with view-read-only before...]
> I set view-read-only to t, then played with a file under RCS.
> When the files is checked in view-mode is turned on, when checking it
> out it's turned off.

> If the code in question is eliminated, view-mode stays turned on after
> checking out.

> There's some code in `after-find-file' (that gets called from
> `revert-buffer') that looks like it does something very similar to the
> code in question here, but `after-find-file' is called with `nomodes' t,
> so that code does not trigger.

So it seems the code is still needed.  Maybe we could/should replace it
with something more clear: E.g. move that code to a new function
`view-refresh' (or whatever else), which we can then call from VC.

Maybe a better option in the longer term is refine the meaning of the
`preserve-modes' arg to revert-buffer, so that some minor modes can
request to be refreshed or not (the VC state is one that would also
benefit from such a change, as can be seen in auto-revert-mode).


        Stefan