unix: update events from pevents between polls

Watchers could be stopped between two `kevent()`/`epoll_wait()` calls
(which may happen in the same loop in `uv__io_poll()`), in such cases
`watcher->events` could be stale and won't be updated to
`watcher->pevents`.

Try to use and rely on `watcher->pevents` instead of blindly expecting
`watcher->events` to be always correct.
test: add regression test for 29fdb3471
fsevents: support japaneese characters in path
unix: fix reopened fd bug

When fd is closed and new one (with the same number) is opened inside
kqueue/epoll/port loop's callback - stale events might invoke callbacks
on wrong watchers.

Check if watcher was changed after invocation and invalidate all events
with the same fd.

fix #826
test
fix test