non-blocking mode: they return None when an operation would block (instead
of raising an exception).

(GNU/Hurd is not dead)

So failed to load tcl/tk dll because $(dist)/tcltk/bin was set to PATH as
relative path. (Windows)

Previous commit changed macpath but macpath is not used anymore as os.path

directly. It used to be built with bzip2's makefile.

Store all errors signaling a disconnection into a global frozenset to save some computation time on recv() and send().

independent of the locale. Set LC_ALL=C too.