* _PyPreConfig_GetGlobalConfig() and _PyCoreConfig_GetGlobalConfig()
now do nothing if the configuration was not initialized with
_PyPreConfig_InitCompatConfig() and _PyCoreConfig_InitCompatConfig()
* Remove utf8_mode=-2 special case: use utf8_mode=-1 instead.
* Fix _PyPreConfig_InitPythonConfig():
* isolated = 0 instead of -1
* use_environment = 1 instead of -1
* Rename _PyConfig_INIT to _PyConfig_INIT_COMPAT
* Rename _PyPreConfig_Init() to _PyPreConfig_InitCompatConfig()
* Rename _PyCoreConfig_Init() to _PyCoreConfig_InitCompatConfig()
* PyInterpreterState_New() now uses _PyCoreConfig_InitPythonConfig()
as default configuration, but it's very quickly overriden anyway.
* _freeze_importlib.c uses _PyCoreConfig_SetString() to set
program_name.
* Cleanup preconfig_init_utf8_mode(): cmdline is always non-NULL.