Closes #15281, #15283: Don't make venv scripts executable, but copy source mode instead, and provide better help for pyvenv.

Issue 14814: The new systematic tests aren't just about error reporting any more - change names accordingly. Added and tweaked some example to ensure they were covering the intended code paths

issue 14826 - Address the buildbot failure quote of url is the required change ( explanation msg164973)

Patch by Brian Brazil.

Patch contributed by Stephen Thorne.

Patch contributed by Stephen Thorne.

Fix 5931 - Python runtime hardcoded in wsgiref.simple_server - Now it specifies an implementation specific term.

earlier without preceding space.

The leak occurred by setting:
echo 1 > /proc/sys/net/ipv6/conf/all/disable_ipv6
before running test_support.

Patch by Brian Brazil.

Issue 14814: Ensure ordering semantics across all 3 entity types in ipaddress are consistent and well-defined

Issue 14814: Explain how to get more error detail in the ipaddress tutorial, and tweak the display for octet errors in IPv4 (noticed the formatting problem when adding to the docs)

Issue 14814: Make the ipaddress code easier to follow by using newer language features (patch by Serhiy Storchaka)