Still lacks docs for Windows (anyone?).

This fixes a regression compared to 2.x, where sys.modules.items()
returns a copy, as indicated by a comment in the source.  Diagnosis and
patch by Erik Tollerud.

It was already the case with Python 2.  However, the corresponding
sys module entries are now set to None (instead of an unusable file object).

Initial patch by Sjoerd de Vries.

Issue #13444: When stdout has been closed explicitly, we should not attempt to flush it at shutdown and print an error.

This also adds a test for issue #5319, whose resolution introduced the issue.

Issue #12856: Ensure child processes do not inherit the parent's random seed for filename generation in the tempfile module.
Patch by Brian Harring.

mention of the CPython optimization hack.

Issue #13458: Fix a memory leak in the ssl module when decoding a certificate with a subjectAltName.
Patch by Robert Xiao.