Fix a rare but potential pre-exec child process deadlock in subprocess on POSIX systems when marking file descriptors inheritable on exec in the child process.  This bug appears to have been introduced in 3.4 with the inheritable file descriptors support.

This also changes Python/fileutils.c `set_inheritable` to use the "slow" two `fcntl` syscall path instead of the "fast" single `ioctl` syscall path when asked to be async signal safe (by way of being asked not to raise exceptions).  `ioctl` is not a POSIX async-signal-safe approved function.

ref: http://pubs.opengroup.org/onlinepubs/9699919799/functions/V2_chap02.html

Documents bpo-15873

now longer -> no longer

`arg_name` and `element_index` are defined as `digit`+ instead of `integer`.

When `__getattr__` is implemented, attribute lookup will always fall back to that,
even if the initial failure comes from `__getattribute__` or a descriptor's `__get__`
method (including property methods).

Add new entries to the widget list.

Changed the definition of width and precision from "integer" to "digit+" in format mini-language doc.

Fix typos found by codespell in docs, docstrings, and comments.

Previously the module name was used, which broke relative imports when pdb was run against a plain module or submodule.

Modify RE examples in documentation to use raw strings to prevent DeprecationWarning.
Add text to REGEX HOWTO to highlight the deprecation.  Approved by Serhiy Storchaka.

* Make sure ``__spec__.loader`` matches ``__loader__`` for namespace packages.
* Make sure ``__spec__.origin` matches ``__file__`` for namespace packages.

https://bugs.python.org/issue32303
https://bugs.python.org/issue32305

This reverts commit 72a0d218.

The reverted commit had a few issues so it was unanimously decided
to undo it. See the bpo issue for details.

Clarify that the level argument is used to determine whether to
perform absolute or relative imports: 0 is absolute, while a positive number
is the number of parent directories to search relative to the current module.

* bpo-32711: Fix warnings for Python/ast_unparse.c

It was deprecated in 3.6.

In the tutorial about the Generator expression, there is an example with
a dict comprehension and not with a generator expression, just removed
the code.

The f-string example for using datetime format specifier does not match the given output.
Changed the format from %b to %B so it matches the output of "January".

Mention only ImportError caused by importing sitecustomize.py/usercustomize.py
themselves will be silently ignored.

When using customized decode error handlers, it is possible for builtin decoders
to write out-of-bounds and then crash.