re PR c++/16965 (Confusing mismatch in error messages)

	PR c++/16965
	* cp-tree.h (qualified_name_lookup_error): Add parameter.
	* name-lookup.c (do_class_using_decl): Restrict set of entities
	passed to cp_emit_debug_info_for_using more carefully.
	(lookup_qualified_name): Allow lookup_member to return sets of
	ambiguous entries.
	* parser.c (cp_parser_lookup_name): Add ambiguous_p parameter.
	(cp_parser_primary_expression): Handle ambiguous lookups.
	(cp_parser_template_name): Adjust use of cp_parser_lookup_name.
	(cp_parser_template_argument): Likewise.
	(cp_parser_elaborate_type_specifier): Likewise.
	(cp_parser_namespace_name): Likewise.
	(cp_parser_class_name): Likewise.
	(cp_parser_lookup_name_simple): Likewise.
	* pt.c (tsubst_qualified_id): Handle ambiguous results.
	(tsubst_expr): Likewise.
	* semantics.c (qualified_name_lookup_error): Add decl paramter.
	For ambiguous lookups, print candidates.

	PR c++/16965
	* g++.dg/parse/error17.C: New test.

From-SVN: r86137