bug#9432: 24.0.50; doc string of `next-error-highlight'

[Drew Adams]

> Permanent highlighting for `next-error-highlight' is a new feature,
> so it should be postponed to 24.2.

Sure, great. But please do not call it "permanent" in the doc.

There would be several times/actions that removed such highlighting; that's all:
next command, next locus change, explicit user command (e.g. `C-0 C-x `'). 

> > The already displayed source buffer should obviously be 
> > used, instead of multiplying things unnecessarily.  Or the
> > behavior should be optional, under user control, and the
> > default should be to show hits in a window already
> > displaying the source buffer.
> 
> This should be customizable with `display-buffer-alist'.

sm> It's optional, controlled by display-buffer-reuse-frames.
sm> The default is nil, largely for historical reasons.

Users should not have to customize anything to get unbugged behavior using emacs
-Q.  If the source file is already showing, why pop it up again in a new window,
by _default_?