PR c++/20293
	* cxx-pretty-print.c (pp_cxx_statement): Print qualifying scopes
	for namespaces.
	(pp_cxx_original_namespace_definition): Likewise.
	* name-lookup.c (ambiguous_decl): Don't issue error messages;
	instead return lists of ambiguous candidates.
	(select_decl): Handle ambiguous namespace lookups.
	* parser.c (cp_token): Add ambiguous_p.
	(cp_lexer_get_preprocessor_token): Set it.
	(cp_parser_diagnose_invalid_type_name): Avoid duplicate messages
	when a qualified name uses an invalid scope. 
	(cp_parser_primary_expression): Print ambiguous candidates.
	(cp_parser_type_parameter): Adjust comment to reflect new
	parameter name for cp_parser_lookup_name.
	(cp_parser_template_argument): Likewise.
	(cp_parser_elaborated_type_specifier): Likewise.
	(cp_parser_namespace_name): Likewise.
	(cp_parser_class_name): Print ambiguous candidates.
	(cp_parser_lookup_name): Rename ambiguous_p parameter to
	ambiguous_decls.  Use it to return a list of ambiguous candiates
	when a lookup is ambiguous.
	(cp_parser_lookup_name_simple): Adjust comment to reflect new
	parameter name for cp_parser_lookup_name.
	
	PR c++/20293
	* g++.dg/parse/ambig4.C: New test.
	* g++.dg/tc1/dr101.C: Adjust error markers.
	* g++.dg/lookup/strong-using-2.C: Likewise.
	* g++.dg/lookup/ambig5.C: Likewise.
	* g++.dg/lookup/ambig4.C: Likewise.
	* g++.dg/parse/crash22.C: Likewise.

From-SVN: r106879