0.26 is broken on Windows (fails to initialize the random number generator)

[mgedmin]

When check-manifest 0.26 tries to run python setup.py sdist in a subprocess, it gets this error on Python 2:

WindowsError: [Error -2146893795] Provider DLL failed to initialize correctly

and the equivalent error on Python 3:

Fatal Python error: Failed to initialize Windows random API (CryptoGen)

This is caused by executing the Python subprocess with an empty(ish) environment (commit 396fda8). See http://bugs.python.org/issue20614, https://code.djangoproject.com/ticket/24160 for details.

My Jenkins caught this.

[mgedmin]

The fix is to always copy %SYSTEMROOT%.

I see the Django project also copies %PATH%, citing http://bugs.python.org/issue8557.

I think I'd better copy the whole os.environ, overriding just PYTHONPATH.