The previous attempt to determine the file?s Content-Length gave a false
positive for pipes on Windows.

Also, drop the special case for sending zero-length iterable bodies.

When the body object is a file, its size is no longer determined with
fstat(), since that can report the wrong result (e.g. reading from a pipe).
Instead, determine the size using seek(), or fall back to chunked encoding
for unseekable files.

Also, change the logic for detecting text files to check for TextIOBase
inheritance, rather than inspecting the ?mode? attribute, which may not
exist (e.g. BytesIO and StringIO).  The Content-Length for text files is no
longer determined ahead of time, because the original logic could have been
wrong depending on the codec and newline translation settings.

Patch by Demian Brecht and Rolf Krahl, with a few tweaks by me.

Some servers send Location header fields with non-ASCII bytes, but "http.
client" requires the request target to be ASCII-encodable, otherwise a
UnicodeEncodeError is raised. Based on patch by Christian Heimes.

Python 2 does not suffer any problem because it allows non-ASCII bytes in the
HTTP request target.

Patch contributed by Chi Hsuan Yen.

Raise ValueError if algorithm is not MD5 or SHA.

Initial patch by Mathieu Dupuy.

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.

Also, remove support.run_doctest() since there is no doctests in
test_urllib2 and urllib.request.

Also, remove support.run_doctest() since there is no doctests in
test_urllib2 and urllib.request.