In some conditions the standard streams will be None or closed in the child process (for example if using "pythonw" instead of "python" on Windows).  Avoid failing with a non-0 exit code in those conditions.

Report and initial patch by poxthegreat.

* Make error message more informative

Replace assertions in error-reporting code with more-informative version that doesn't cause confusion over where and what the error is.

* Additional clarification + get travis to check

* Change from SystemError to TypeError

As suggested in PR comment by @pitrou, changing from SystemError; TypeError appears appropriate.

* NEWS file installation; ACKS addition (will do my best to justify it by additional work)

* Making current AssertionErrors in multiprocessing more informative

* Blurb added re multiprocessing managers.py, queues.py cleanup

* Further multiprocessing cleanup - went through pool.py

* Fix two asserts in multiprocessing/util.py

* Most asserts in multiprocessing more informative

* Didn't save right version

* Further work on multiprocessing error messages

* Correct typo

* Correct typo v2

* Blasted colon... serves me right for trying to work on two things at once

* Simplify NEWS entry

* Update 2017-08-18-17-16-38.bpo-5001.gwnthq.rst

* Update 2017-08-18-17-16-38.bpo-5001.gwnthq.rst

OK, never mind.

* Corrected (thanks to pitrou) error messages for notify

* Remove extraneous backslash in docstring.

* bpo-30794: added kill() method to multiprocessing.Process

* Added entries to documentation and NEWS

* Refactored test_terminate and test_kill

* Fix SIGTERM and SIGKILL being used on Windows for the tests

* Added "versionadded" marker to the documentation

* Fix trailing whitespace in doc

* Fix bpo-30596: Add close() method to multiprocessing.Process

* Raise ValueError if close() is called before the Process is finished running

* Add docs

* Add NEWS blurb

* Fix bpo-30589: improve Process.exitcode with forkserver

When the child is killed, Process.exitcode should return -signum, not 255.

* Add Misc/NEWS

* bpo-16500: Allow registering at-fork handlers

* Address Serhiy's comments

* Add doc for new C API

* Add doc for new Python-facing function

* Add NEWS entry + doc nit

This allows different parts of a program to use different methods for
starting processes without interfering with each other.

are now created non-inheritable; add functions os.get/set_inheritable(),
os.get/set_handle_inheritable() and socket.socket.get/set_inheritable().

See http://hg.python.org/sandbox/sbt#spawn