Make TTCs work. Fixes #710.

Make TTCs work.  Fixes #710.

The code did not handle face indices; it relied on the PS name and the
(physical) font name only.  No visible changes for users.  However,
`ly:pango-font-physical-fonts' now returns a three-element list instead of a
pair, but I doubt that this function makes sense outside of
`framework-ps.scm'.