* dwarf2read.c (die_specification, dwarf2_extension, follow_die_ref):
Make the dwarf2_cu * parameter output as well as input. Update it if
we follow a reference to another CU.
(read_func_scope, determine_class_name, namespace_name, dwarf2_attr)
(die_type, die_containing_type): Update calls to changed functions.
Use the returned CU along with the returned DIE.
(read_namespace): Use dwarf2_attr instead of dwarf2_extension.