bpo-31009: Fix support.fd_count() on Windows

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On Windows, test.support.fd_count() now calls
msvcrt.CrtSetReportMode() to not kill the process nor log any error
on stderr on os.dup(fd) if the file descriptor is invalid.

https://bugs.python.org/issue31009

[vstinner]

I tested manually: test_child_fd_inflation() of test_multiprocessing_spawn doesn't hang anymore on a debug build on Windows. Moreover, test_regrtest still pass.

" continuous-integration/appveyor/pr — AppVeyor was unable to build non-mergeable pull request" I don't understand this error :-( My commit is just on top on master. I updated my local Git clone, there is no new commt in master.

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I ran manually the test suite on Windows: all tests pass. To be honest, test_distutils fails, but it's unrelated to this change and I don't know how to fix my Windows support to get a working C compiler...

[vstinner]

"AppVeyor was unable to build non-mergeable pull request" : "To rebuild that PR you can close and then re-open it."
http://help.appveyor.com/discussions/problems/4830-stuck-on-appveyor-was-unable-to-build-non-mergeable

[vstinner]

Crap, there was a whitespace issue... "Fixing Python file whitespace ... 1 file: Lib/test/support/init.py". It's now fixed.

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Travis CI failed on downloading Python 3.6 on the docs job :-(

Downloading archive: https://s3.amazonaws.com/travis-python-archives/binaries/ubuntu/14.04/x86_64/3.6-python.tar.bz2
$ sudo tar xjf python-3.6.tar.bz2 --directory /
bzip2: (stdin) is not a bzip2 file.