Move the _loop attribute from the constructor of _SelectorTransport,
_ProactorBasePipeTransport and _UnixWritePipeTransport classes to the
constructor of the _FlowControlMixin class.

Add also an assertion to explicit that the parent class must ensure that the
loop is defined (not None)

Patch by Alex Gaynor with some modifications by me.

and above.  Patch by Tim Graham.

"xmlcharrefreplace", and "surrogatepass" error handlers.

executables used to find the mac address, with /sbin and /usr/sbin as
fallbacks.

Issue #11508: Fixed uuid.getnode() and uuid.uuid1() on environment with
virtual interface.  Original patch by Kent Frazier.

Issue #18784: The uuid module no more attempts to load libc via ctypes.CDLL,
if all necessary functions are already found in libuuid.
Patch by Evgeny Sologubov.

Issue #16102: Make uuid._netbios_getnode() work again on Python 3.