Issue 10591: test_os failure in refleak runs

$ ./python -m test.regrtest -R 3:2 test_os
[1/1] test_os
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beginning 5 repetitions
12345
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test test_os failed -- Traceback (most recent call last):
  File "/home/antoine/py3k/__svn__/Lib/test/test_os.py", line 898, in test_unicode_name
    self._test_link(self.file1, self.file2)
  File "/home/antoine/py3k/__svn__/Lib/test/test_os.py", line 879, in _test_link
    os.link(file1, file2)
OSError: [Errno 17] File exists