bug#56393: Actually fix the long lines display bug

[Gregory Heytings]

> > Is this better/clearer: "Increase the counter more for a large 
> > modification and less for a small modification.  Increase it 
> > logarithmically to avoid increasing it too much."?
>
> Sounds good, thanks.

Now done.

I also made a few (final?) tweaks.  Please tell me if the feature is ready 
to land on master, or if further improvements are needed.