Implement nested namespace definitions.

Implement nested namespace definitions.

/cp
2015-09-18  Ville Voutilainen  <ville.voutilainen@gmail.com>

	Implement nested namespace definitions.
	* parser.c (cp_parser_namespace_definition): Grok nested namespace
	definitions.

/testsuite
2015-09-18  Ville Voutilainen  <ville.voutilainen@gmail.com>

	Implement nested namespace definitions.
	* g++.dg/cpp1z/nested-namespace-def1.C: New.
	* g++.dg/cpp1z/nested-namespace-def2.C: Likewise.
	* g++.dg/cpp1z/nested-namespace-def3.C: Likewise.
	* g++.dg/lookup/name-clash5.C: Adjust.
	* g++.dg/lookup/name-clash6.C: Likewise.

From-SVN: r227932