Return a list copy in #'built-in-face-specifiers, pre-empting modification.
2008-12-21 Aidan Kehoe <kehoea@parhasard.net>
* faces.c (Fbuilt_in_face_specifiers):
Don't simply warn the user not to modify
Vbuilt_in_face_specifiers, enforce this by returning a copy of the
list.