bug#6091: 23.1.96; fringe face can not be remapped

[Chong Yidong]

Leo <sdl.web@gmail.com> writes:

> 1. emacs -Q
> 2. paste the following into *scratch*
>
>   (push '(fringe (:foreground "#71d3b4" :background
>                   "#233323"))
>         face-remapping-alist)
>
> 3. C-j (not C-x C-e)

This is because the Emacs redisplay engine doesn't repaint the parts of
the screen unless it has changed, and it has no way to know that you've
changed the variable `face-remapping-alist'.  You can order a refresh by
calling `redraw-display'.

We could set up a more elaborate system for the redisplay engine to keep
track of `face-remapping-alist', but I don't think it's warranted, and
it may slow down the much more common case where `face-remapping-alist'
never changes.  Instead, I will update the doc of `face-remapping-alist'
to mention this issue.