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 These functions have been replaced by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().

Fix the following warning on Windows:

parser\tokenizer.c(1297): warning C4244: 'function': conversion from
'__int64' to 'int', possible loss of data.

The test failed on my laptop because the busy loop took 15.9 ms
whereas the test expects at least 20 ms. Modify test_process_time()
as test_thread_time() has been modified recently: only require 15 ms
instead of 20 ms.

Rework _PyCoreConfig_Read() function which *reads* core configuration
to not *modify* the path configuration.

A new _PyCoreConfig_SetPathConfig() function now recreates the path
configuration from the core configuration. This function is now
called very late in _Py_InitializeCore(), just before calling
initimport().

Changes:

* Add _PyCoreConfig.dll_path
* Py_SetPath() now fails with a fatal python error on memory
   allocation failure.
* Rename _PyPathConfig_Calculate() to _PyPathConfig_Calculate_impl()
* Replace _PyPathConfig_Init() with _PyPathConfig_Calculate(): the
  function now requires a _PyPathConfig
* Add _PyPathConfig_SetGlobal() to set the _Py_path_config global
  variable.
* Add _PyCoreConfig_InitPathConfig(): compute the path configuration
* Add _PyCoreConfig_SetPathConfig(): set path configuration from core
  configuration
* Rename wstrlist_append() to _Py_wstrlist_append()
* _Py_wstrlist_append() now handles integer overflow.

The parentheses were incorrect.

Py_Main() can again be called after Py_Initialize(), as in Python
3.6. The new configuration is ignored, except of
_PyMainInterpreterConfig.argv which is used to update sys.argv.

Increase the timeout: give timeout x 4 instead of timeout x 2 to
threads to wait until the Event is set, but reduce the sleep from 500
ms to 250 ms. So the test should be more reliable and faster!

On Windows, sometimes test_signal.test_warn_on_full_buffer() fails to
fill the socketpair buffer. In that case, the C signal handler
succeed to write into the socket, it doesn't log the expected send
error, and so the test fail.

On Windows, the test now uses a timeout of 50 ms to fill the
socketpair buffer to fix this race condition.

Other changes:

* Begin with large chunk size to fill the buffer to speed up the
  test.
* Add error messages to assertion errors to more easily identify
  which assertion failed.
* Don't set the read end of the socketpair as non-blocking.