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

[Artur Malabarba]

>> Have you tested redisplay-would-scroll-window-p in a fully folded
>> org-mode buffer with 100 headlines where each headline has 100 lines
>> of content?
>
> Of course not.  :-)
>
> By the way, what does Isearch do with such org-mode folded buffer?  Does
> it unfold the content, ever?

Isearch has an option for that. By default it searches inside hidden
text, and reveals the hidden text if the match is in there.

But that's not why I asked.

The 'count-screen-lines' function can be horribly slow on a large
number of lines. I just want to check whether 'move-to-window-line'
doesn't suffer from the same issue. A huge org buffer with lots of
folded headlines is just a common cause of slowness for
`count-screen-lines' because small visual movements could mean very
large actual movements.