This will make it easier to clean up channels (e.g. when used in tests).

Patch by Thomas Jones.

`obj.async` is now a syntax error, so the warning/shim is
quasi-unnecessary.

The editline emulation needs to be initialized *after* the name is
defined. This fixes the long open issue.

Only gcmodule.c uses _PyGC_REFS* macros now.
This makes easy to read GC code.

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.