Ensure that directory file descriptors refer to directories different
from the current directory, and that src_dir_fd and dst_dir_fd refer
to different directories.
Add context manager open_dir_fd() in test.support.os_helper.
Currently we freeze several modules into the runtime. For each of these modules it is essential to bootstrapping the runtime that they be frozen. Any other stdlib module that we later freeze into the runtime is not essential. We can just as well import from the .py file. This PR lets users explicitly choose which should be used, with the new "-X frozen_modules=[on|off]" CLI flag. The default is "off" for now.
https://bugs.python.org/issue45020
Serhiy Storchaka
Eric Snow
Hai Shi