Issue2574

In this build job https://travis-ci.org/jythontools/jython/jobs/213994211 test_tarfile failed, this test also seems a bit unreliable maybe it should be investigated?

I'll add it (again) to the list of shame in regrtest.

I get unclosed file problems on Windows and I can make it fail if I run it enough times:

dist\bin\jython -m test.regrtest test_tarfile test_tarfile test_tarfile test_tarfile test_tarfile test_tarfile test_tarfile test_tarfile
...
test_tarfile
C:\Users\Jeff\Documents\Eclipse\jython-trunk\dist\Lib\test\test_tarfile.py:1667: UserWarning: Failed to remove C:\Users\Jeff\Documents\Eclipse\jython-trunk\$test_1_tmp
  warnings.warn("Failed to remove "+TEMPDIR)
test test_tarfile failed -- Traceback (most recent call last):
  File "C:\Users\Jeff\Documents\Eclipse\jython-trunk\dist\Lib\test\test_tarfile.py", line 203, in test_ignore_zeros
    tar = tarfile.open(tmpname, mode="r", ignore_zeros=True)
  File "C:\Users\Jeff\Documents\Eclipse\jython-trunk\dist\Lib\tarfile.py", line 1665, in open
    raise ReadError("file could not be opened successfully")
ReadError: file could not be opened successfully

See also #2316, and the several skips or special logic related to a different behaviour of umask permissions simulated on Windows. Some of this comes from the CPython version. A clean and consistent solution is partly a question of what we ought to *expect* from Jython on Windows.