bug#17453: Framework extending window functions for Follow Mode (etc.).

[Juri Linkov]

> ...., I now think the best name would be the last of these three,
> window-group-start.  It is not too long, and the phrase "window_group"
> fits in with all the primitives apart from `recenter'.  So we'd need some
> different naming ideas, perhaps "recenter-group" or "group-recenter".

For consistency with other related names it could have the same prefix, e.g.
"window-group-recenter".

> By the way, have you had the chance to look at the changes I made to
> isearch.el in the scratch/follow branch?

One thing in the isearch-related part of your patch that I'm not excited about
is the macro isearch-call-message.  With Stefan's request there is no need in it
since it becomes one-liner: (funcall isearch-message-function).

Another thing that disturbs me is moving lazy-highlighting checks
to a new function isearch-lazy-highlight-maybe-new-loop.

What do you think about moving only window-checking into new function
i.e. only checks for window-start/window-end/etc that need (sit-for 0)
and leaving other checks in isearch-lazy-highlight-new-loop?
Would this help to avoid new problems such as un-highlighting
postponed until the timer fires?