Issue #27955: modify py_getrnadom() and dev_urandom()

* Add comments from Python 3.7
* PEP 7 style: add {...}

 (Patch by Xiang Zhang)

I forgot there two variations of os.stat() in Python 3.5.

Patch by Eryk Sun.

Also update the classmethod and staticmethod doc strings and comments to
match the RST documentation.

Issue #25270: Prevent codecs.escape_encode() from raising SystemError when an empty bytestring is passed

Patch by Gergely Imreh and Markus Holtermann.

Patch by Mark Williams.

Patch by INADA Naoki.

Patch by iceboy.

Patch by Seth Michael Larson.

Patch by Kevin Conway.

Backport of 01ddd608b85c.

zipimport should use the same optimization level as the interpreter.

A newer instance of this option, enabled in the configure script when
building outside the source tree, made this redundant.