Multi-phase initialized modules allow m_traverse to be called while the
module is still being initialized, so module authors may need to account
for that.

(cherry picked from commit e32bbaf376a09c149fa7c7f2919d7c9ce4e2a055)

Creating backup files with ~ suffix can be undesirable in some environment,
such as when building RPM packages. Instead of requiring the user to remove
those files manually, option -n was added, that simply disables this feature.

-n was selected because 2to3 has the same option with this behavior.

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withdrawn, Kees Blom's railroad program has been lost to the sands of time for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