* src/abg-ir.cc (dynamic_type_hash::operator()): Handle hashing of
a pointer to an instance of typedef_decl.
(typedef_decl::typedef_decl, typedef_decl::operator==)
(typedef_decl::operator==, typedef_decl::get_underlying_type)
(typedef_decl::~typedef_decl): New definitions.
* src/abg-ir.h (class typedef_decl, struct typedef_decl_hash): New
declarations.
* src/abg-reader.cc (handle_typedef_decl): New definition.
(handle_element): Handle de-serialization of typedef-decl element.
* src/abg-writer.cc (write_typedef_decl): New definition.
(write_decl): Handle serialization of an instance of typedef_decl.
* tests/data/test-read-write/test7.xml: New test.
* tests/Makefile.am: Add it to the distribution.
* tests/test-read-write.cc: De-serialize the content of the new
test, serialize it back and diff both.
