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.

consisting of non-constants: `x in [a, b]` and `for x in [a, b]`.
The case of all constant elements already was optimized.

and remove redundant code.

A StopAsyncIteration raised on assigning or unpacking will be now propagated
instead of stopping the iteration.

* Skip write()/data_received() if sslpipe is destroyed

`int` fails back to `__trunc__` is `__int__` isn't defined, so cover
that in the docs.

Replace example result of "5 through 9" with complete list: "5, 6, 7, 8, 9".
This format is more consistent with the surrounding examples.

* fix a typo: documention -> documentation
* fix the type of IPv?Network.hostmask
* add documentation about IPv?Network.netmask
* fix IPv6Network constructor doc that extended netmasks are not supported

Fix a crash on fork when using a custom memory allocator (ex: using
PYTHONMALLOC env var).

_PyGILState_Reinit() and _PyInterpreterState_Enable() now use the
default RAW memory allocator to allocate a new interpreters mutex on
fork.

The length in strncpy is one char too short and as a result it leads
to a build warning with gcc 8.  Comment out the strncpy since the
interpreter aborts immediately after anyway.

* bpo-32991: Add test capturing expectation.

DocTestFinder.find should return an empty list for doctests in a namespace package.

* bpo-32991: Restore expectation that inspect.getfile on a namespace package raises TypeError.

Like Python, IDLE optionally runs one startup file in the Shell window
before presenting the first interactive input prompt.  For IDLE,
option -s runs a file named in environmental variable IDLESTARTUP or
PYTHONSTARTUP; -r file runs file.  Python sets __file__ to the startup
file name before running the file and unsets it before the first
prompt.  IDLE now does the same when run normally, without the -n
option.

* Prevent low-grade poplib REDOS (CVE-2018-1060)

The regex to test a mail server's timestamp is susceptible to
catastrophic backtracking on long evil responses from the server.

Happily, the maximum length of malicious inputs is 2K thanks
to a limit introduced in the fix for CVE-2013-1752.

A 2KB evil response from the mail server would result in small slowdowns
(milliseconds vs. microseconds) accumulated over many apop calls.
This is a potential DOS vector via accumulated slowdowns.

Replace it with a similar non-vulnerable regex.

The new regex is RFC compliant.
The old regex was non-compliant in edge cases.

* Prevent difflib REDOS (CVE-2018-1061)

The default regex for IS_LINE_JUNK is susceptible to
catastrophic backtracking.
This is a potential DOS vector.

Replace it with an equivalent non-vulnerable regex.

Also introduce unit and REDOS tests for difflib.
Co-authored-by: Tim Peters <tim.peters@gmail.com>
Co-authored-by: Christian Heimes <christian@python.org>