Issue #20311, #20452: poll and epoll now round the timeout away from zero,

Issue #20311, #20452: poll and epoll now round the timeout away from zero,
instead of rounding towards zero, in select and selectors modules:
select.epoll.poll(), selectors.PollSelector.poll() and
selectors.EpollSelector.poll(). For example, a timeout of one microsecond
(1e-6) is now rounded to one millisecondi (1e-3), instead of being rounded to
zero.

Mention the change in Misc/NEWS.