Allow partial specialization of variable templates.

Allow partial specialization of variable templates.

	* cp-tree.h (TINFO_USED_TEMPLATE_ID): New.
	* decl.c (duplicate_decls): Copy it.
	* error.c (dump_decl) [TEMPLATE_ID_EXPR]: Handle variables.
	* parser.c (cp_parser_decltype_expr): Do call finish_id_expression
	on template-ids.
	* pt.c (register_specialization): Remember variable template insts.
	(instantiate_template_1): Find the matching partial specialization.
	(check_explicit_specialization): Allow variable partial specialization.
	(process_partial_specialization): Likewise.
	(push_template_decl_real): Likewise.
	(more_specialized_partial_spec): Rename from more_specialized_class.
	(most_specialized_partial_spec): Rename from most_specialized_class.
	(get_partial_spec_bindings): Rename from get_class_bindings.

From-SVN: r218104