bug#23574: 24.5; Overzealous underlining in emacs-nox

[martin rudalics <rudalics@gmx.at>]

 > Going back to the bug report, there's still one issue to consider:
 > should we add underline (and then also overline and strikethrough) to
 > the list of face attributes that cause face extension on GUI frames.
 > The logic behind the current code seems to be to extend attributes
 > that are related to background of the text.  The above 3 seem to be a
 > kind-of background, so maybe we should add them.

It would make my life much easier if face extension were, in general,
customizable.  I would immediately turn it off everywhere.

My motivation is that I have font-lock distinguish things like comments
and strings mainly by their background face.  Since these look awful
when extending to the end of a window, I have to provide my own
‘font-lock-fontify-syntactically-region’ function which assures that
newline characters within strings and comments never get the
corresponding face.  This consumes resources and, for example, disallows
using text properties to skip the rest of a comment or a string.  It
goes without saying, that my version of this function is never in synch
with the one of the repository.

I also use separate background colors for editable fields, buttons,
links and the like which also look awful when spanning two or more
lines.  No font-locking can help me here.

martin