User-created types with wrong __new__ can be instantiated

GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2018-08-08.19:07:33.344>
labels = ['interpreter-core', '3.8', 'type-bug', '3.7']
title = 'User-created types with wrong __new__ can be instantiated'
updated_at = <Date 2018-08-09.17:52:28.761>
user = 'https://github.com/pppery'

bugs.python.org fields:

activity = <Date 2018-08-09.17:52:28.761>
actor = 'ppperry'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Interpreter Core']
creation = <Date 2018-08-08.19:07:33.344>
creator = 'ppperry'
dependencies = []
files = []
hgrepos = []
issue_num = 34362
keywords = []
message_count = 4.0
messages = ['323297', '323299', '323336', '323347']
nosy_count = 5.0
nosy_names = ['ncoghlan', 'eric.snow', 'serhiy.storchaka', 'ppperry', 'Vadim Pushtaev']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue34362'
versions = ['Python 2.7', 'Python 3.6', 'Python 3.7', 'Python 3.8']