PR c++/67074 - namespace aliases

PR c++/67074 - namespace aliases

	PR c++/67074 - namespace aliases
	* decl.c (duplicate_decls): Don't error here on mismatched
	namespace alias.
	* name-lookup.c (name_lookup::add_value): Matching namespaces are
	not ambiguous.
	(diagnose_name_conflict): Namespaces are never redeclarations.
	(update_binding): An alias can match a real namespace.

	PR c++/67074
	* g++.dg/lookup/pr67074.C: New.
	* g++.dg/parse/namespace-alias-1.C: Adjust.

From-SVN: r249408