This fix is a superset of the functionality introduced by the issue #19494
enhancement, and supersedes that fix.  Instead of a new handler, we have a new
password manager that tracks whether we should send the auth for a given uri.
This allows us to say "always send", satisfying #19494, or track that we've
succeeded in auth and send the creds right away on every *subsequent* request.
The support for using the password manager is added to AbstractBasicAuth,
which means the proxy handler also now can handle prior auth if passed
the new password manager.

Patch by Akshit Khurana, docs mostly by me.

Patch by Michael McFadden, with a few small style tweaks.

CID 1294331 (#1 of 1): Identical code for different branches (IDENTICAL_BRANCHES)

Remove redundant check for tb != NULL to shut up Coverity . It has been set to Py_None a couple of lines earlier.
CID 1291697 (#1 of 1): Dereference before null check (REVERSE_INULL)
check_after_deref: Null-checking tb suggests that it may be null, but it has already been dereferenced on all paths leading to the check.

accepting bytes, bytearrays, and buffers is now consistent with
both the documentation and the implementation.

module binaries, with a platform triple of just "darwin", resulting in
file names like:

    _ssl.cpython-35m-darwin.so

rather than just _ssl.so as previously.

Instead of attempting to encode differences in CPU architecture and OS X
deployment targets in the file name as is done on other platforms,
these continue to be managed by the use of Apple multi-architecture
("fat") files, by the system dynamic loader, and by logic in higher-levels
like sysconfig.get_platform() and pip.

Patch by Demian Brecht.

Patch by Arnon Yaari.

  the architecture triplet in the extension name, to make it easy to test builds
  for different ABIs in the same working tree.

more consistent API than the existing call* functions.
(enhancement from issue 23342)

end lines from the code object, fixing an issue when a lambda function is
used as decorator argument.  Patch by Thomas Ballinger.

Patch by Jamiel Almeida.

Patch by Jacinda Shelly.

of the Python io module and the C io module.  They do not currently
match so the failing test is marked with @unittest.skip.