bug#17453: Isearch doesn't work properly with Follow Mode.

[Juri Linkov]

>> >>From another perspective, settings lazy-highlight-buffer to t
>> (implemented in bug#21092) and removing the current restriction of
>> (overlay-put ov 'window (selected-window)) will lazy-highlight matches
>> in all follow windows with no effort.
>
> I wasn't actually aware of that fix.
>
> There were three main problems my patch fixed:
> 1) Searching commands were restricted to a single follow window.  This
> was caused by the lazy highlighting mechanism, as you say.
> 2) Lazy highlighting was only being done in a single window.
> 3) In scrolling commands, point was restricted to the singled window,
> rather than being able to move freely throughout all the windows.

IIUC, lazy highlighting is not a problem anymore, so the remaining
problem is how to switch windows when the next search position
happens to be in an adjacent window.  Since there is no other
core library that require so much changes to adapt to follow-mode,
and there are already some mode-specific hooks in follow.el like
compilation-filter-hook, indicates that it's the responsibility of follow.el
to support isearch in follow-mode.  So I believe the right way to do
this is like Artur presented in a short patch, and maybe it's possible
to simplify it even more by using isearch-update-post-hook with
a follow-align-compilation-windows like hook.  I mean something like
(add-hook 'isearch-update-post-hook follow-align-isearch-windows t t)