bug#21092: 25.0.50; Option `lazy-highlight-max-at-a-time' does not work

[Drew Adams <drew.adams@oracle.com>]

> OK, great to hear.  So this is a real Isearch bug, and there is a
> possibility for it to be fixed.
> 
> Hopefully someone knowledgable will contribute to a solution.
> I can try to help, but it would be great if Juri or someone else
> who understands the code well could lead.

OK, I think I found the problem.  I have something working, but
will send it in the form of a patch in a while.

Essentially, it is the isearch.el code itself that imposes, in
a few places, not searching past (window-end) or before
(window-start), regardless of the value of
`isearch-lazy-highlight-max-at-a-time'.  This is what needs to
be fixed, to be (point-max) and (point-min) when
`isearch-lazy-highlight-max-at-a-time' is nil.

A more thoroughgoing fix would take into account a numeric
value of `isearch-lazy-highlight-max-at-a-time', but I won't
bother with that, for now.