[2.7] bpo-30243: Fixed the possibility of a crash in _json. (GH-1420) (#1471)

It was possible to get a core dump by using uninitialized
_json objects. Now __new__ methods create initialized objects.
__init__ methods are removed..
(cherry picked from commit 76a3e51a403bc84ed536921866c86dd7d07aaa7e)
2 files changed