Add more tests for subinterpreters. This patch also fixes a few small defects in the channel implementation.

* test_ssl: Remove skip_if_broken_ubuntu_ssl

We no longer support OpenSSL 0.9.8.15.15.

* bpo-28167: Remove platform.linux_distribution

* bpo-24318: Rewrite the README PGO section.

Merged from a phone on an airplane. :)

This condition as already tested before this code is called.

To be more consistent with other code (and so people stop hassling me!), reflow the dataclasses comments to not use a single space indentation when continuing a paragraph of text.

This is an initial version that likely requires much polishing. I'm adding it lay out the structure and so we have something to start working from.

The ssl module now contains OP_NO_RENEGOTIATION constant, available with
OpenSSL 1.1.0h or 1.1.1.

Note, OpenSSL 1.1.0h hasn't been released yet.
Signed-off-by: Christian Heimes <christian@python.org>

Don't crash on warnings.warn_explicit() if module_globals is not a dict.

Added to the eye-verified htest, not to the unittests.
Also remove some stray leftover comments.

Also bump PendingDeprecationWarning to DeprecationWarning.

Instead of passing configure args such as --without-gcc or --with-icc,
instead prefer to rely on the native way of finding the compiler:
passing CC (or CPP or CXX depending).

This allows configure to find the correct compiler instead of having to
be explicitly told. It also more correctly builds on both macOS and
FreeBSD since the system compiler is used by default (cc)

bpo-33497: Add errors param to cgi.parse_multipart and make an encoding in FieldStorage use the given errors (GH-6804)

https://bugs.python.org/issue32769

Most of the parameters were added in 3.4.4 (b9bf913a), but this
change was not documented

Clarify that flush is implied when the call to write contains a newline character.