Move the code to run tests in multiple processes using threading and subprocess
to a new submodule.
Move also slave_runner() (renamed to run_tests_slave()) and
run_test_in_subprocess() (renamed to run_tests_in_subprocess()) there.
with attributes and methods.
The --threshold command line option is now ignored if the gc module is missing.
* Convert main() variables to Regrtest attributes, document some attributes
* Convert accumulate_result() function to a method
* Create setup_python() function and setup_regrtest() method.
* Import gc at top level
* Move resource.setrlimit() and the code to make the module paths absolute into
the new setup_python() function. So this code is no more executed when the
module is imported, only when main() is executed. We have a better control on
when the setup is done.
* Move textwrap import from printlist() to the top level.
* Some other minor cleanup.
Victor Stinner