Reimplement qualified namespace lookup.

Reimplement qualified namespace lookup.

	* name-lookup.c (name_lookup::flags): New member.  Adjust ctor.
	(name_lookup::ambiguous, name_lookup::add_value)
	name_lookup::add_type, name_lookup::process_binding): New.
	(name_lookup::search_namespace_only)
	name_lookup::search_namespace, name_lookup::search_usings): New.
	(name_lookup::search_qualified): New.
	(do_nonmember_using_decl, suggest_alternatives_for)
	lookup_qualified_name): Adjust.
	(tree_vec_contains): Delete.
	(qualified_lookup_using_namespace): Rename to ...
	(qualified_namespace_lookup): ... here.  Reimplement.
(((--This line, and those below, will be ignored--

M    cp/name-lookup.c
M    cp/ChangeLog

From-SVN: r248462