(font_vconcat_entity_vectors): New function.

(font_vconcat_entity_vectors): New function.
(struct font_sort_data): New member font_driver_preference.
(font_compare): Check font_driver_preference.
(font_sort_entities): The format of the first argument changed.
(font_delete_unmatched): Likewise.
(font_list_entities): The return type changed.
(font_select_entity): The format of the second argument changed.
(font_find_for_lface): Adjusted for the above changes.  Don't
suppress the checking of C even if the repertory supports it.
(Flist_fonts): Adjusted for the above changes.