bug#21481: 24.5; show-paren-mode does not work with --color=no

[Eli Zaretskii]

> From: Simon Gerraty <sjg@juniper.net>
> Date: Mon, 14 Sep 2015 12:31:59 -0700
> 
> I've noticed in recent versions of Emacs that paren matching does not
> work.
> 
> Turns out it *does* work, but I cannot see the result, because emacs is
> started with --color=no (sorry but I cannot stand the color stuff)
> 
> If I start emacs without that paren matching works - using cyan
> to highlight open paren.
> 
> That would suggest that the face used for show-paren-match is wrong -
> ignoring color=no.

Thanks, I modified the definition of show-paren-match face to use
underline on color-less displays.