decl.c (poplevel): Check DECL_INITIAL invariant.

decl.c (poplevel): Check DECL_INITIAL invariant.

	* decl.c (poplevel): Check DECL_INITIAL invariant.
	(duplicate_decls): Preserve DECL_INITIAL when eliminating
	a new definition in favour of an old declaration.
	(start_preparsed_function): Define and document value of
	DECL_INITIAL before and after routine.
	(finish_function): Check DECL_INITIAL invariant.
	* parser.c
	(cp_parser_function_definition_from_specifiers_and_declarator):
	Skip duplicate function definitions.

From-SVN: r119427