Add CPython posixpath + tests
Add minimal posix stubs
Add minimal pwd stubs
Add CPython genericpath + tests
posixpath: Refactor a twice-imported module
posixpath: Refactor multiple imports in a scope
posixpath. Add 'any' type annotations
posixpath: Refactor except with multiple types
test.test_posixpath: Refactor static method
test_posixpath: Comment out dynamic func replace

Force related test cases to fail.
test_genericpath: Add 'any' type annotations
test_genericpath: Refactor set literal
test_genericpath: Refactor multiple types in except
Add unittest.skipIf to stubs
Minor update to os module stubs
Add CPython random + tests
test_random: Refactor complex literal
genericpath: Work around import problem
posixpath: Work around import problem

For some reason, references to os.error are not valid. It may be related
to build ordering, i.e. os may be semantically analyzed too late in the
build.
Add minimal stubs for _random