add pipe2() to the os module

Lib/test/test_posix.py

 "Test posix functions"
 
 from test import support
 
 # Skip these tests if there is no posix module.
 posix = support.import_module('posix')
 
 import errno
 import sys
 import time
@@ skipping 463 matching lines @@
             reader, writer = posix.pipe()
             os.close(reader)
             os.close(writer)
 
     @unittest.skipUnless(hasattr(os, 'pipe2'), "test needs os.pipe2()")
     @support.requires_linux_version(2, 6, 27)
     def test_pipe2(self):
         self.assertRaises(TypeError, os.pipe2, 'DEADBEEF')
         self.assertRaises(TypeError, os.pipe2, 0, 0)
 
-        # try calling without flag, like os.pipe()
-        r, w = os.pipe2()
+        # try calling with flags = 0, like os.pipe()
+        r, w = os.pipe2(0)
         os.close(r)
         os.close(w)
 
         # test flags
         r, w = os.pipe2(os.O_CLOEXEC|os.O_NONBLOCK)
         self.addCleanup(os.close, r)
         self.addCleanup(os.close, w)
         self.assertTrue(fcntl.fcntl(r, fcntl.F_GETFD) & fcntl.FD_CLOEXEC)
         self.assertTrue(fcntl.fcntl(w, fcntl.F_GETFD) & fcntl.FD_CLOEXEC)
         # try reading from an empty pipe: this should fail, not block
@@ skipping 318 matching lines @@
 
 
 def test_main():
     try:
         support.run_unittest(PosixTester, PosixGroupsTester)
     finally:
         support.reap_children()
 
 if __name__ == '__main__':
     test_main()