* src/abg-ir.h (class reference_type_def, struct pointer_type_def)
(struct reference_type_def): New declaration.
(type_base_hash::operator(), type_decl_hash::operator())
(scope_type_decl_hash::operator())
(qualified_type_def_hash::operator()): Include the typeid name in
the hash.
* src/abg-ir.cc (reference_type_def::reference_type_def)
(reference_type_def::operator==)
(reference_type_def::get_pointed_to_type)
(reference_type_def::is_lvalue)
(reference_type_def::~reference_type_def): New definitions.
(dynamic_type_hash::operator): Hash pointer_type_def and
reference_type_def instances.
* src/abg-reader.cc (read_context::finish_decl_creation)
(read_context::finish_type_decl_creation)
(handle_reference_type_def): New definitions.
(read_file): Handle "reference-type-def" elements.
(handle_type_decl, handle_namespace_decl)
(handle_qualified_type_decl, handle_pointer_type_def): Use the new
read_context::finish_type_decl_creation or
read_context::finish_decl_creation.
* src/abg-writer.cc (write_reference_type_def): New definition.
(write_decl): Supporting writing a pointer to an instance of
reference_type_def.
* tests/data/test-read-write/test5.xml: New test file.
* tests/test-read-write.cc: (De)Serialize it.
* tests/Makefile.am: Add it to the build system.
