3d highlights on dark colors

[Miles Bader]

The way emacs calculates the highlight colors for the `3d' effect -- it
basically just scales the reference color by a fixed factor -- works
pretty well for brightish colors (like the default menubar & mode-line
colors, for instance).

However, the darker the reference color gets, the less well this works,
and for dark-but-not-that-dark colors (e.g., "grey30"), it's quite hard
to see the highlight.  This is especially a problem for the `Options'
menu, which uses 3d-boxes to indicate option settings, and definitely
presents a problem if such boxes aren't visible.

So I'd like to checkin the attached code, which increases the highlight
scaling factor for darker colors.  It works pretty well for those dark
colors I've tried, and should have no effect at all when the default
faces are used.

Any objections?

-Miles

dark-boost.patch
Description: Patch to boost 3d highlights on dark colors

-- 
Love is a snowmobile racing across the tundra.  Suddenly it flips over,
pinning you underneath.  At night the ice weasels come.  --Nietzsche