add better workaround system for processes when there is no console.

[Vizonex]

What do these changes do?

This change does a better job at providing a workaround when there is no standard stdin, stdout, stderr inputs by checking if _fileno(...) is -2 which is the safest way to perform this, It's better than the old method written around 2 days ago for 0.6.1's release. It is related to #126 but I still refuse to do the full subprocess.py implemenation assuming it would make my pull request to uvloop all that much more difficult which I did not see as being an option unless I'm forced to. Using devnull is a much more reliable choice in which it doesn't become of game of juggling file descriptors around and doesn't use a global variable to determine if there isn't a console (which that can be unreliable if these items were changed by the end user or developer).

Note

If your wondering as to why I'm refusing to write things the way subprocess.py has the fds open and close when items are None is that I have to merge this code back to the uvloop fork I have anyways which is already a pain to resync these up so if your wondering why I'm do not want to do the full setup. There's your reason.

Are there changes in behavior for the user?

Users should now expect less unusual behaviors with pyinstaller and cxfreeze or other exe builders when attempting to launch a subprocess.

Is it a substantial burden for the maintainers to support this?

Related issue number

Checklist

• I think the code is well written
• Unit tests for the changes exist
• Documentation reflects the changes