Fix reverting the default face to standard/themed state in GUIs

Fix reverting the default face to standard/themed state in GUIs

* lisp/cus-edit.el (custom-face-set, custom-face-mark-to-save)
(custom-face-save): Record the default (standard or themed) attributes
of the default face in a symbol property.
(custom-face-reset-saved, custom-face-mark-to-reset-standard): When
reverting the default face to the standard or themed state, use the
default attributes we recorded, instead of relying in the defface spec
of the default face, since that doesn't give enough information to
reset all attributes, like foreground, family, etc (bug#14635).