* fhandler.cc (fhandler_base::set_flags): Set was_nonblocking if the
O_NONBLOCK flag has been specified.
(fhandler_base_overlapped::close): Check for was_nonblocking instead
of for is_nonblocking. Explain why.
(fhandler_base::set_nonblocking): Set was_nonblocking if noblocking
mode gets enabled.