Windows: Process.terminate() may raise AccessDenied if process already died

[giampaolo]

This is something which also used to affect the subprocess module:
http://bugs.python.org/issue14252

Appveyor failure:
https://ci.appveyor.com/project/giampaolo/psutil/build/job/36xyueo57wdc17bm

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ERROR: psutil.tests.test_process.TestProcess.test_cwd
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Traceback (most recent call last):
  File "c:\projects\psutil\psutil\tests\test_process.py", line 84, in tearDown
    reap_children()
  File "c:\projects\psutil\psutil\tests\__init__.py", line 446, in reap_children
    p.terminate()
  File "c:\projects\psutil\psutil\__init__.py", line 354, in wrapper
    return fun(self, *args, **kwargs)
  File "c:\projects\psutil\psutil\__init__.py", line 1311, in terminate
    self._proc.kill()
  File "c:\projects\psutil\psutil\_pswindows.py", line 635, in wrapper
    raise AccessDenied(self.pid, self._name)
AccessDenied: psutil.AccessDenied (pid=1388)
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ERROR: psutil.tests.test_process.TestProcess.test_name
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Traceback (most recent call last):
  File "c:\projects\psutil\psutil\tests\test_process.py", line 84, in tearDown
    reap_children()
  File "c:\projects\psutil\psutil\tests\__init__.py", line 446, in reap_children
    p.terminate()
  File "c:\projects\psutil\psutil\__init__.py", line 354, in wrapper
    return fun(self, *args, **kwargs)
  File "c:\projects\psutil\psutil\__init__.py", line 1311, in terminate
    self._proc.kill()
  File "c:\projects\psutil\psutil\_pswindows.py", line 635, in wrapper
    raise AccessDenied(self.pid, self._name)
AccessDenied: psutil.AccessDenied (pid=2008)
======================================================================
ERROR: psutil.tests.test_unicode.TestFSAPIsWithInvalidPath.test_proc_name
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Traceback (most recent call last):
  File "c:\projects\psutil\psutil\tests\test_unicode.py", line 152, in tearDown
    reap_children()
  File "c:\projects\psutil\psutil\tests\__init__.py", line 446, in reap_children
    p.terminate()
  File "c:\projects\psutil\psutil\__init__.py", line 354, in wrapper
    return fun(self, *args, **kwargs)
  File "c:\projects\psutil\psutil\__init__.py", line 1311, in terminate
    self._proc.kill()
  File "c:\projects\psutil\psutil\_pswindows.py", line 635, in wrapper
    raise AccessDenied(self.pid, self._name)
AccessDenied: psutil.AccessDenied (pid=2848)
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