Make it clear that setting __class__ on a module has worked since 3.5,
but support for __getattr__ and __dir__ on module instances requires 3.7+

Patch by Cheryl Sabella.

The nismodule is now compatible with new libnsl and headers location
Signed-off-by: Christian Heimes <christian@python.org>

Since context.c is compiled with Py_BUILD_CORE, using a macro
will result in a slightly more optimal code.

When an unawaited coroutine is collected very late in shutdown --
like, during the final GC at the end of PyImport_Cleanup -- then it
was triggering an interpreter abort, because we'd try to look up the
"warnings" module and not only was it missing (we were prepared for
that), but the entire module system was missing (which we were not
prepared for).

I've tried to fix this at the source, by making the utility function
get_warnings_attr robust against this in general. Note that it already
has the convention that it can return NULL without setting an error,
which is how it signals that the attribute it was asked to fetch is
missing, and that all callers already check for NULL returns.

There's a similar check for being late in shutdown at the top of
warn_explicit, which might be unnecessary after this fix, but I'm not
sure so I'm going to leave it.

* Document `from __future__ import annotations`
* Provide plumbing and tests for `from __future__ import annotations`
* Implement unparsing the AST back to string form

This is required for PEP 563 and as such only implements a part of the
unparsing process that covers expressions.

dictview_repr(): Use a Py_ReprEnter() / Py_ReprLeave() pair to check
for recursion, and produce "..." if so.

test_recursive_repr(): Check for the string rather than a
RecursionError.  (Test cannot be any tighter as contents are
implementation-dependent.)

test_deeply_nested_repr(): Add new test, replacing the original
test_recursive_repr().  It checks that a RecursionError is raised in
the case of a non-recursive but deeply nested structure.  (Very
similar to what test_repr_deep() in test/test_dict.py does for a
normal dict.)

OrderedDictTests: Add new test case, to test behavior on OrderedDict
instances containing their own values() or items().

Reported by Coverity Scan.

Global variables should not used as import target.
Use temporary variable instead.

Patch by Bo Bayles.

* bpo-32662: Implement Server.start_serving() and Server.serve_forever()

New methods:

* Server.start_serving(),
* Server.serve_forever(), and
* Server.is_serving().

Add 'start_serving' keyword parameter to loop.create_server() and
loop.create_unix_server().

The refleak in question wasn't really important, as context vars
are usually created at the toplevel and live as long as the interpreter
lives, so the context var name isn't ever GCed anyways.

Some tests failed when the PATH environment variable contained a path
to an existing file. Fix tests to ignore also NotADirectoryError, not
only FileNotFoundError and PermissionError.

`object_pairs_hook=OrderedDict` idiom is deprecated.

Add two new private APIs: _PyObject_LookupAttr() and _PyObject_LookupAttrId()

In Py_Main(), don't call pymain_set_global_config() early: only call
it when the whole configuration has been read.

Add an unit test to prevent future regression.

* Add timezone to datetime C API

* Add documentation for timezone C API macros

* Add dedicated tests for datetime type check macros

* Remove superfluous C API test

* Drop support for TimeZoneType in datetime C API

* Expose UTC singleton to the datetime C API

* Update datetime C-API documentation to include links

* Add reference count information for timezone constructors

To support reproducible builds, the setting of of SOURCE_DATE_EPOCH triggers the py_compile module -- and by extension, compileall -- to forcibly compile with hash-based .pyc files. This eliminates the possibility of timestamp-based .pyc files which vary between builds.

* Rename sock_sendfile test methods
* Make sock_sendfile tests more stable

* bpo-32651 - In the documentation for os.getlogin(), recommend getpass.getuser()

Specifically, it's not possible to subclass Task/Future classes
and override the following methods:

* Future._schedule_callbacks
* Task._step
* Task._wakeup

_PyCoreConfig_Read() is now responsible to compute sys.path.
So sys.path is now computed before calling _Py_InitializeCore().

Changes:

* Add module_search_path, module_search_paths, executable, prefix,
  base_prefix, exec_prefix and base_exec_prefix to _PyCoreConfig.
* _PyMainInterpreterConfig_Read() now only converts wchar_t** lists
  into a Python list, it doesn't compute sys.path anymore.

Makefile $MACHDEPPATH uses $PLATDIR, but this variable was removed.
So remove also $MACHDEPPATH.

Remove also $EXTRAMACHDEPPATH.