bug#56815: 29.0.50; Isearch lazy-highlight highlights too much when truncate-lines is in effect

[Gregory Heytings]

> > So if no good ideas arise that are simple enough to implement, I'm okay 
> > with simply disabling isearch-lazy-highlight in such buffers, as I 
> > wrote in the original bug report.  (Doing that will probably require 
> > exposing the "long-lines" flag to Lisp, but that's fine by me.)
>
> Exposing the "long-lines" flag to Lisp is exactly what is needed.

My current plan is to run a hook when long lines are detected, in which 
modes such as isearch will be free to add any function they like.