Original patch by Alexander Belopolsky.  Patch by Skip Montanaro.

* Add a test for frozen with unhashable field value.
* Improve a comment.

This removes a hack and replaces it with a proper
mapping {'list': 'List', 'dict': 'Dict', ...}.

Different paths are executed for normal exit and for leaving
the 'async with' block with 'break', 'continue' or 'return'.

This makes performance better and produces shorter pickles. This change is backwards compatible up to the oldest currently supported version of Python (3.4).

Py_UNICODE is deprecated since Python 3.3.
But the deprecation is missed in the c-api/arg document.

when __aenter__() or __aexit__() return non-awaitable object.

Followup to primary PR for the issue, GH-6344.

A 'u' string prefix cannot be paired with either 'r' or 'f'.  Consistently
color as much of the prefix, starting at the right, as is valid.

Build and link with private copy of Tcl/Tk 8.6 for the macOS 10.6+
installer. The 10.9+ installer variant already does this.  This means that
the Python 3.7 provided by the python.org macOS installers no longer need or
use any external versions of Tcl/Tk, either system-provided or user-
installed, such as ActiveTcl.

Most of them have been added in 3.7.

Forcing the macOS IDLE.app gui process to launch in 32-mode was
a necessary hack for old versions of Tk (Aqua Carbon as in Tk 8.4
and early versions of 8.5); it is not needed for current versions
of Tk.  Since 32-bit launching will no longer be supported on
future releases of macOS, allow IDLE.app to launch in 64-bit mode.

* Also in docs

test_asyncio hangs indefinitely on macOS 10.13.2+ on `read_pty_output()`
using the KqueueSelector. Closing `proto.transport` (as is done in
`write_pty_output()`) seems to fix it.
(cherry picked from commit 12f74d8608c15cacd9d5786524e2be9ca36f007e)
Co-authored-by: Nathan Henrie <n8henrie@users.noreply.github.com>

Also, re-enable test_read_pty_output on macOS.

This also fixes python/typing#512
This also fixes python/typing#511

As was discussed in both issues, some typing forms deserve to be treated
as immutable by copy and pickle modules, so that:
* copy(X) is X
* deepcopy(X) is X
* loads(dumps(X)) is X  # pickled by reference

This PR adds such behaviour to:
* Type variables
* Special forms like Union, Any, ClassVar
* Unsubscripted generic aliases to containers like List, Mapping, Iterable

This not only resolves inconsistencies mentioned in the issues, but also
improves backwards compatibility with previous versions of Python
(including 3.6).

Note that this requires some dances with __module__ for type variables
(similar to NamedTuple) because the class TypeVar itself is define in typing,
while type variables should get module where they were defined.

https://bugs.python.org/issue32873

bpo-32844: subprocess: Fix a potential misredirection of a low fd to stderr.

When redirecting, subprocess attempts to achieve the following state:
each fd to be redirected to is less than or equal to the fd
it is redirected from, which is necessary because redirection
occurs in the ascending order of destination descriptors.
It fails to do so in a couple of corner cases,
for example, if 1 is redirected to 2 and 0 is closed in the parent.

This is part of PEP 487 and the descriptor protocol.