* 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.

glibc is deprecating libcrypt in favor of libxcrypt, however python assumes
that crypt.h will always be included. This change makes the header inclusion
explicit when libxcrypt is present on the system.

* bpo-32618: Fix test_mutatingdecodehandler not testing test.mutating

It should test both test.replacing and test.mutating instead of test test.replacing twice.

"python3 -bb -Wd" now works as expected:
"python3 -bb -Wd -Werror::BytesWarning" is no more needed.

Update configure since configure.ac was modified to drop support for
FreeBSD 4.

PyUnicode_DecodeLocaleAndSize(), PyUnicode_DecodeLocale() and
PyUnicode_EncodeLocale() now use always use the UTF-8 encoding on
Android, instead of the current locale encoding.

On Android API 19, mbstowcs() and wcstombs() are broken and cannot be
used.

Drop support of FreeBSD 9 and older.

* bpo-31801:  Enum:  add _ignore_ as class option

_ignore_ is a list, or white-space seperated str, of names that will not
be candidates for members; these names, and _ignore_ itself, are removed
from the final class.

* bpo-31801:  Enum:  add documentation for _ignore_

* bpo-31801: Enum: remove trailing whitespace

* bpo-31801: Enum: fix bulleted list format

* bpo-31801: add version added for _ignore_