Surprisingly there were almost no tests for keyword arguments in subclasses.

PR 26456 makes checks for some classes (like tuple, list, frozenset) more strict: if subclass does not define __init__ or __new__, it will reject arbitrary keyword arguments.

It also makes the check in set.__init__() more lenient for uniformity with frozenset and list. Subclass of set can now define a __new__() method with additional keyword parameters without overriding also __init__().

Added tests for some of builtin classes.

Raymond, please take a look. It touches classes maintained tracked by you: set/frozenset, itertools, random.