implement start_new_session.

gevent/subprocess.py

@@ -284,7 +284,6 @@ class Popen(object):
             else:
                 close_fds = False
 
-
         if mswindows:
             if preexec_fn is not None:
                 raise ValueError("preexec_fn is not supported on Windows "
@@ -1017,6 +1016,9 @@ class Popen(object):
                                     if sig is not None:
                                         signal.signal(sig, signal.SIG_DFL)
 
+                            if start_new_session:
+                                os.setsid()
+
                             if env is None:
                                 os.execvp(executable, args)
                             else:

greentest/patched_tests_setup.py

@@ -218,9 +218,6 @@ if sys.version_info[:2] >= (3, 4):
         # Our monkey patch waits for the process with a watcher and so detects
         # the exit before the normal polling mechanism would
 
-        'test_subprocess.POSIXProcessTestCase.test_start_new_session',
-        # XXX: We don't implement the start_new_session option yet
-
         'test_subprocess.POSIXProcessTestCase.test_exception_bad_args_0',
         'test_subprocess.POSIXProcessTestCase.test_exception_bad_executable',
         'test_subprocess.POSIXProcessTestCase.test_exception_cwd',