re PR c++/25836 (G++ does not allow a conversion of templated types)

	PR c++/25836
	* cp-tree.h (push_class_stack): New function.
	(pop_class_stack): Likewise.
	* class.c (class_stack_node): Add hidden field.
	(pushclass): Clear it.
	(push_class_stack): New function.
	(pop_class_stack): Likewise.
	(currently_open_class): Ignore hidden classes.
	(currently_open_derived_class): Likewise.
	* name-lookup.c (push_to_top_level): Call push_class_stack.
	(pop_from_top_level): Call pop_class_stack.
	PR c++/25836
	* g++.dg/template/init6.C: New test.

From-SVN: r109945