bug#4710: 23.1.50; Bad display of underlines crossing line boundaries

[Drew Adams]

> >> "If it hurts, don't do that" comes to mind.

To my mind also, FWIW.

> > But it does look really ugly.  :-)  This single behavioural 
> > tic is what makes underlines undesirable.  If somebody had
> > a good idea how to fix this in general, that would be a win.
> 
> Maybe someone could come up with a neater way to display "face
> continuations" (face that applies to the text where a line is
> wrapped).  For underline, we could put a short bit of dotted underline
> as in:
>               foo bar baz
>                   -------?
>               toto titi turlu
>              ?----

Why assume that underlined whitespace should not show an underline?
Likewise for other face attributes.

Down that path lies dwimmadness.

At the very least, any such fiddling should be done only for indentation (i.e.,
in the code that indents text).  And it certainly should be under user control
(e.g., optional).