This is a slight rework of my previous patch, incorporating some
suggestions.

Now the remapping is strictly only for display -- if lisp code wants to
know about it, it has to look at the variable (`face-remapping-alist').

[It would probably be good if such functions as describe-face and perhaps
customize-face would display a note when invoked on a remapped face.]

BTW one very nice use I've found is for reading mail in gnus:

   (defun use-variable-pitch-default-face ()
     (set (make-local-variable 'face-remappings)
          '((default variable-pitch))))

   (add-hook 'gnus-article-mode-hook 'use-variable-pitch-default-face)



Patch: