Fixes handling of leading dots.

Patch by Serhiy Storchaka.

This fixes the following warning when building the docs (probably from
the commit for issue #14901):

"/Doc/faq/windows.rst:138: WARNING: undefined label: setting-envvars (if the
link has no caption the label must precede a section header)"

This adds to the work done for issue #15990 (i.e. f44b8d69e5fc and the
commits referenced there).

Patch Serhiy Storchaka.

Patch by Anton Kasyanov.

Fix Issue15701 - HTTPError info method call raises AttributeError. Fix that to return headers correctly

Patch by Serhiy Storchaka.

Thanks to Inada Naoki

Patch by Serhiy Storchaka.

Fix issue #16646: ftplib.FTP.makeport() might lose socket error details.  (patch by Serhiy Storchaka)

Patch by Ashish Nitin Patil.

Issue #16626: Fix infinite recursion in glob.glob() on Windows when the pattern contains a wildcard in the drive or UNC path.
Patch by Serhiy Storchaka.

Patch by Sebastian Kreft.

Issue #16298: In HTTPResponse.read(), close the socket when there is no Content-Length and the incoming stream is finished.
Patch by Eran Rundstein.

compiler logic will do the right thing with just x as a Py_uhash_t.  This
matches what was already done in the 3.3 version.

cleanup only - no functionality or hash values change.

computation as the overflow behavior of signed integers is undefined.

In practice we require compiling everything with -fwrapv which forces overflow
to be defined as twos compliment but this keeps the code cleaner for checkers
or in the case where someone has compiled it without -fwrapv or their
compiler's equivalent.

Found by Clang trunk's Undefined Behavior Sanitizer (UBSan).

Cleanup only - no functionality or hash values change.