Message 322366 - Python tracker

TODO list, open questions:

* Should isolated=1 always imply config->ignore_environment=1 and config->user_site_directory = 0?
* Should we rename debug to parser_debug? "debug" is a very generic term, whereas this flag is really specific to the parser
* Remove _Py_CheckHashBasedPycsMode: replace it with config._check_hash_pycs_mode?