* class.c (check_bases): Diagnose derivation from a final class.
	* cp-tree.h (lang_type_class): Add is_final and adjust dummy.
	(CLASSTYPE_FINAL): New.
	* parser.c (cp_parser_class_head): Parse class-virt-specifier, set
	CLASSTYPE_FINAL.
	* pt.c (instantiate_class_template_1): Copy CLASSTYPE_FINAL.

From-SVN: r173761