Issue #18571: Implementation of the PEP 446: file descriptors and file handles

are now created non-inheritable; add functions os.get/set_inheritable(),
os.get/set_handle_inheritable() and socket.socket.get/set_inheritable().

Lib/test/test_tempfile.py

@@ -333,6 +333,7 @@ class TestMkstempInner(BaseTestCase):
             v="q"
 
         file = self.do_create()
+        self.assertEqual(os.get_inheritable(file.fd), False)
         fd = "%d" % file.fd
 
         try: