bug#56682: Fix the long lines font locking related slowdowns

[Gregory Heytings]

> > > If you for some reason prefer to keep that branch active, can you 
> > > please merge the current master to it, so that the changes in 
> > > narrow-to-region will be on the branch?
> >
> > Is that feasible?  Non fast forwards are not allowed in the Emacs 
> > repository, so rebasing a feature branch is not possible (without using 
> > the workaround of deleting and recreating the branch).
>
> I didn't mean a rebase, I meant a merge.

Indeed, I did not read what you wrote with enough attention.  Sorry for 
that.