This allows findsource() to work in doctests.

A patch from Dirkjan Ochtman.

methods.

Original patch by Erik Bray.

Original patch by Erik Bray.

Original patch by Erik Bray as part of #11595, changed by me to improve
readability.

Original patch by Tshepang Lekhonkhobe.

Just try to open files from the ZIP for reading, don't extract them to avoid
UnicodeEncodeError if the filename is not encodable to the filesystem encoding
(e.g. ASCII locale encoding).

The new tests now requires pthread_sigmask(). Skip the test if the function is
missing, e.g. if Python is compiled without threads.

Block the signal before calling sigwait(). Use os.fork() to ensure that we have
only one thread.

Initial patch written by Charles-François Natali.

packaging.util.check_environ will define HOME and PLAT if they don’t exist; for
some reason, it does not define PLAT when running the tests from a checkout (so
no regrtest warning) but does when running from an installed Python.

Cleaning up the envvar in test_dist fixes the warning on my machine, but I
suspect that a test runner using a different order to run files or running them
in parallel may have PLAT defined in its environment because of another test.
Quite a lot of code ends up calling check_environ; maybe we should just clean
up PLAT in every test.  For now I’m doing this simple fix, we’ll see if we get
bug reports.

The code does not write checksum or file length for .pyc and .pyo in the RECORD
file, in compliance with PEP 376, but the test forgot to take .pyo into
account.  This was not caught because there were no .pyo in the checkout, but
after installing there are .pyo files created by compileall, and the test picks
them up.