Failure on Windows 10 with Python 3.7 beta 3:

======================================================================
ERROR: test_pcbuild_rt (test.test_regrtest.ProgramsTestCase)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "C:\Users\vstinner\AppData\Local\Programs\Python\Python37\lib\test\test_regrtest.py", line 602, in test_pcbuild_rt
    self.run_batch(script, *rt_args, *self.regrtest_args, *self.tests)
  File "C:\Users\vstinner\AppData\Local\Programs\Python\Python37\lib\test\test_regrtest.py", line 577, in run_batch
    proc = self.run_command(args)
  File "C:\Users\vstinner\AppData\Local\Programs\Python\Python37\lib\test\test_regrtest.py", line 475, in run_command
    **kw)
  File "C:\Users\vstinner\AppData\Local\Programs\Python\Python37\lib\subprocess.py", line 453, in run
    with Popen(*popenargs, **kwargs) as process:
  File "C:\Users\vstinner\AppData\Local\Programs\Python\Python37\lib\subprocess.py", line 756, in __init__
    restore_signals, start_new_session)
  File "C:\Users\vstinner\AppData\Local\Programs\Python\Python37\lib\subprocess.py", line 1155, in _execute_child
    startupinfo)
FileNotFoundError: [WinError 2] The system cannot find the file specified


We may just skip the test if the script is not installed.