New tests also added.

I also made the comments in line with the builtin Grammar/Grammar. PEP 306 was
withdrawn, Kees Blom's railroad program has been lost to the sands of time for
at least 16 years now (I found a python-dev post from people looking for it).

Co-authored-by: Vajrasky Kok <sky.kok@speaklikeaking.com>

fstat may block for long time if the file descriptor is on a
non-responsive NFS server, hanging all threads. Most fstat() calls are
handled by _Py_fstat(), releasing the GIL internally, but but
_Py_fstat_noraise() does not release the GIL, and most calls release the
GIL explicitly around it.

This patch fixes last 2 calls to _Py_fstat_no_raise(), avoiding hangs
when calling:
- mmap.mmap()
- os.urandom()
- random.seed()

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.