This commit also removes a couple of non-standard status codes. They were
added as part of edf669b13482, so there is no backwards compatibility issue.

Patch by Demian Brecht.

Elsewhere in the setobject.c code we do a bitwise-and with the mask
instead of using a conditional to reset to zero on wrap-around.
Using that same technique here use gives cleaner, faster, and more
consistent code.

duplicated addresses and simplify the code.

Issue 23261:  Clean-up the hack to store the set.pop() search finger in a hash field instead of the setobject.

portable representation.

Issue #23266: Much faster implementation of ipaddress.collapse_addresses() when there are many non-consecutive addresses.

Patch by Al Sweigart.

getaddrinfo("localhost") can fail depending on the name server configuration,
use "127.0.0.0" instead.

Issue #21817: When an exception is raised in a task submitted to a ProcessPoolExecutor, the remote traceback is now displayed in the parent process.
Patch by Claudiu Popa.

Patch by Nikolaus Rath and Martin Panter.

Only happened with oddly capitalized debug executables on Windows.
Patch by Claudiu Popa.

Patch by Jon Dufresne.

Override the connect_read_pipe() method of the loop to mock immediatly
pause_reading() and resume_reading() methods.

The test failed randomly on FreeBSD 9 buildbot and on Windows using trollius.

StreamWriter: close() now clears the reference to the transport

StreamWriter now raises an exception if it is closed: write(), writelines(),
write_eof(), can_write_eof(), get_extra_info(), drain().

Closes #23160: Respect the environment variable SVNROOT in external-common.bat (patch by anselm.kruis)

* Use test_utils.run_briefly() to execute pending calls to really close
  transports
* sslproto: mock also _SSLPipe.shutdown(), it's need to close the transport
* pipe test: the test doesn't close explicitly the PipeHandle, so ignore
  the warning instead
* test_popen: use the context manager ("with p:") to explicitly close pipes