Fixed-pitch and variable-pitch faces

[Chong Yidong]

I've been trying to debug a problem that I've been seeing with
`fixed-pitch' and `variable-pitch' faces, which is that they aren't
anti-aliased, unlike the rest of the faces used by Emacs.  It seems that
these faces are defined with the "courier" and "helv" families, as
follows:

(defface fixed-pitch
  '((t :family "courier"))
  "The basic fixed-pitch face."
  :group 'basic-faces)

(defface variable-pitch
  '((t :family "helv"))
  "The basic variable-pitch face."
  :group 'basic-faces)

I think the font backend is matching these to non-fontconfig fonts.

It seems to me that the default Emacs fonts should attempt to define a
font family, now that we have the new font backend.  I propose to remove
the :family entries to these faces, but am not sure how to redefine
these faces.  In other words, how should `fixed-pitch' and
`variable-pitch' be distinguished from `default'?

Any thoughts?