* Inline cmdline_get_env_flags() into config_read_env_vars():
  _PyCoreConfig_Read() now reads much more environment variables like
  PYTHONVERBOSE.
* Allow to override faulthandler and allocator even if dev_mode=1.
  PYTHONMALLOC is now the priority over PYTHONDEVMODE.
* Fix _PyCoreConfig_Copy(): copy also install_signal_handlers,
  coerce_c_locale and coerce_c_locale_warn
* _PyCoreConfig.install_signal_handlers default is now 1: install
  signals by default
* Fix also a compiler warning: don't define _PyPathConfig type twice.

Enable and fix SMTPUTF8SimTests in test_smtplib.

The tests for SMTPUTF8SimTests in test_smtplib.py were not actually
being run because test_smtplib was still using the 'test_main' pattern,
and the class was never added to test_main.

Additionally, one of the tests needed to be moved to the non-UTF8 server
class because it relies on the server not being UTF-8 compatible (and it
had a bug in in).

PYTHONTRACEMALLOC=0 environment variable and -X tracemalloc=0 command
line option are now allowed to disable explicitly tracemalloc at
startup.

On Windows, passing a negative value to local results in an OSError because localtime_s on Windows does not support negative timestamps. Unfortunately this means that fold detection for timestamps between 0 and max_fold_seconds will result in this OSError since we subtract max_fold_seconds from the timestamp to detect a fold. However, since we know there haven't been any folds in the interval [0, max_fold_seconds) in any timezone, we can hackily just forego fold detection for this time range on Windows.

* Fix case-sensitive comparison

test_nt_helpers assumed that two versions of a Windows path could be compared case-sensitively. This is not the case, and the difference can be triggered (apparently) by running the test on a path somewhere below a Junction.

* Move _PyMain.main_importer_path inside pymain_run_python
* If main_importer_path is non-NULL, update sys.path[0] earlier

* If _Py_InitializeCore() is called twice, the second call now copies
  and apply (partially) the new configuration.
* Rename _Py_CommandLineDetails to _PyCmdline
* Move more code into pymain_init(). The core configuration created
  by Py_Main() is new destroyed before running Python to reduce the
  memory footprint.
* _Py_InitializeCore() now returns the created interpreter.
  _Py_InitializeMainInterpreter() now expects an interpreter.
* Remove _Py_InitializeEx_Private(): _freeze_importlib now uses
  _Py_InitializeFromConfig()
* _PyCoreConfig_InitPathConfig() now only computes the path
  configuration if needed.

Add more fields to _PyCoreConfig:

* _check_hash_pycs_mode
* bytes_warning
* debug
* inspect
* interactive
* legacy_windows_fs_encoding
* legacy_windows_stdio
* optimization_level
* quiet
* unbuffered_stdio
* user_site_directory
* verbose
* write_bytecode

Changes:

* Remove pymain_get_global_config() and pymain_set_global_config()
  which became useless. These functions have been replaced by
  _PyCoreConfig_GetGlobalConfig() and
  _PyCoreConfig_SetGlobalConfig().
* sys.flags.dont_write_bytecode value is now restricted to 1 even if
  -B option is specified multiple times on the command line.
* PyThreadState_Clear() now uses the config from the current
  interpreter rather than using global Py_VerboseFlag

The script will exit with the number 0 (zero), instead of the letter O.

* _PyCoreConfig: add isolated and site_import attributes
* Replace Py_IgnoreEnvironment with config->ignore_environment when
  reading the current configuration
* _PyCoreConfig_Read() now sets ignore_environment, utf8_mode,
  isolated and site_import from Py_IgnoreEnvironment, Py_UTF8Mode,
  Py_IsolatedFlag and Py_NoSiteFlag
* _Py_InitializeCore() now sets Py_xxx flags from the configuration
* pymain_read_conf() now uses _PyCoreConfig_Copy() to save/restore
  the configuration.
* Rename _disable_importlib of _PyCoreConfig to _install_importlib
* _PyCoreConfig_SetGlobalConfig() now also set
  Py_HashRandomizationFlag
* Replace !Py_NoSiteFlag with core_config->site_import

Now base64.Error is always raised instead of UnboundLocalError or
OverflowError.

Also make getchildren() and getiterator() emitting
a DeprecationWarning instead of PendingDeprecationWarning.

Improve consistency with the signature for sorted(), heapq.nsmallest(), heapq.nlargest(), and itertools.groupby().

Fix error messages for PySequence_Size(), PySequence_GetItem(),
PySequence_SetItem() and PySequence_DelItem() called with a mapping
and PyMapping_Size() called with a sequence.

imaplib now allows MOVE command in IMAP4.uid() (RFC 6851:
IMAP MOVE Extension) and potentially as a name of supported
method of IMAP4 object.

When Python is installed on Windows, python -m test test_tools failed
because it tried to run Tools\scripts\2to3.py which requires an
argument. Skip this script. On other platforms or on Windows but when
run from source code (not installed), the script is called "2to3"
instead of "2to.py" and so was already skipped.

Modify also the unit test to unload all modules which have been
loaded by the test.

Previously, Python was built in 32-bit mode and so issues specific to
64-bit mode like compiler warnings could be missed.

* _PyCoreConfig_Read() no longer directly modifies Py_IsolatedFlag
  and Py_NoSiteFlag global configuration flags. The function now
  requires two pointers to integer, so these flags can be set later,
  to avoid side effets in _PyCoreConfig_Read().
* pathconfig_global_init() now leaves Py_IsolatedFlag and
  Py_NoSiteFlag unchanged.
* Fix pathconfig_global_init(): avoid computing the path
  configuration twice, use _PyCoreConfig_SetPathConfig().