Explicitly document C functions and C variables that can be set
before Py_Initialize().

This flag was deprecated and wasn't used anymore since Python 2.0.

The paragraph that contains example of string literal concatenation was placed
after the section about concatenation using the '+' sign.
Moved the paragraph to the appropriate section.

The test.support.skip_unless_bind_unix_socket() decorator is used to skip
asyncio tests that fail because the platform lacks a functional bind()
function for unix domain sockets (as it is the case for non root users on the
recent Android versions that run now SELinux in enforcing mode).

The previous behavior was to raise an exception

    NotImplementedError: result of type 0

when the value of the property is VT_EMPTY.

bpo-32096, bpo-30860:  Partially revert the commit
2ebc5ce4:

* Move structures back from Include/internal/mem.h to
  Objects/obmalloc.c
* Remove _PyObject_Initialize() and _PyMem_Initialize()
* Remove Include/internal/pymalloc.h
* Add test_capi.test_pre_initialization_api():
   Make sure that it's possible to call Py_DecodeLocale(), and then call
   Py_SetProgramName() with the decoded string, before Py_Initialize().

PyMem_RawMalloc() and Py_DecodeLocale() can be called again before
_PyRuntimeState_Init().
Co-Authored-By: Eric Snow <ericsnowcurrently@gmail.com>

Previously, 'msilib.OpenDatabase()' function raised a
cryptical exception message when it couldn't open or
create an MSI file. For example:

    Traceback (most recent call last):
      File "<stdin>", line 1, in <module>
    _msi.MSIError: unknown error 6e

Move footnote markers to be closer to the related terminology:
before the end of the sentence, instead of after.

* Minor wording tweaks

The Distribution class now explicitly raises an
exception when 'classifiers', 'keywords' and
'platforms' fields are not specified as a list.

create_filter() now expects the action as a _Py_Identifier which
avoids string comparison, and more important, to avoid handling the
"unknown action" annoying case.

* calculate_path() rewritten in Modules/getpath.c and PC/getpathp.c
* Move global variables into a new PyPathConfig structure.
* calculate_path():

  * Split the huge calculate_path() function into subfunctions.
  * Add PyCalculatePath structure to pass data between subfunctions.
  * Document PyCalculatePath fields.
  * Move cleanup code into a new calculate_free() subfunction
  * calculate_init() now handles Py_DecodeLocale() failures properly
  * calculate_path() is now atomic: only replace PyPathConfig
    (path_config) at once on success.

* _Py_GetPythonHomeWithConfig() now returns an error on failure
* Add _Py_INIT_NO_MEMORY() helper: report a memory allocation failure
* Coding style fixes (PEP 7)

* Py_Main() now reads the PYTHONHOME environment variable
* Add _Py_GetPythonHomeWithConfig() private function
* Add _PyWarnings_InitWithConfig()
* init_filters() doesn't get the current core configuration from the
  current interpreter or Python thread anymore. Pass explicitly the
  configuration to _PyWarnings_InitWithConfig().
* _Py_InitializeCore() now fails on _PyWarnings_InitWithConfig()
  failure.
* Pass configuration as constant

Move _PyCoreConfig.module_search_path_env to _PyMainInterpreterConfig
structure.

Adds a simpler and faster alternative to ExitStack for handling
single optional context managers without having to change the
lexical structure of your code.

Patch mostly by Cheryl Sabella

Changes:

* Py_Main() initializes _PyCoreConfig.module_search_path_env from
  the PYTHONPATH environment variable.
* PyInterpreterState_New() now initializes core_config and config
  fields
* Compute sys.path a little bit ealier in
  _Py_InitializeMainInterpreter() and new_interpreter()
* Add _Py_GetPathWithConfig() private function.

* Optimize warnings.filterwarnings(). Replace re.compile('') with
  None to avoid the cost of calling a regex.match() method, whereas
  it always matchs.
* Optimize get_warnings_attr(): replace PyObject_GetAttrString() with
  _PyObject_GetAttrId().

Cleanup also create_filter():

* Use _Py_IDENTIFIER() to allow to cleanup strings at Python
  finalization
* Replace Py_FatalError() with a regular exceptions

* Rename support._match_test() to support.match_test(): make it
  public
* Remove support.match_tests global variable. It is replaced with a
  new support.set_match_tests() function, so match_test() doesn't
  have to check each time if patterns were modified.
* Rewrite match_test(): use different code paths depending on the
  kind of patterns for best performances.
Co-Authored-By: Serhiy Storchaka <storchaka@gmail.com>

Add one last minor clarification for idpattern

* should not be more verbose if the code is correct
* enabled checks can be "expensive"

Py_Main() now handles two more -X options:

* -X showrefcount: new _PyCoreConfig.show_ref_count field
* -X showalloccount: new _PyCoreConfig.show_alloc_count field

The developer mode (-X dev) now creates all default warnings filters
to order filters in the correct order to always show ResourceWarning
and make BytesWarning depend on the -b option.

Write a functional test to make sure that ResourceWarning is logged
twice at the same location in the developer mode.

Add a new 'dev_mode' field to _PyCoreConfig.

Modify subprocess._args_from_interpreter_flags() to handle -X dev
option.

Add also unit tests for test.support.args_from_interpreter_flags()
and test.support.optim_args_from_interpreter_flags().

When Python is build is debug mode (Py_DEBUG), DeprecationWarning,
PendingDeprecationWarning and ImportWarning warnings are now
displayed by default.

test_venv: run "-m pip" and "-m ensurepip._uninstall" with -W
ignore::DeprecationWarning since pip code is not part of Python.

The line number in correct when using the -x option: Py_Main() uses
ungetc() to not skip the first newline character.

The new -X dev command line option now also enables asyncio debug
mode.