kernel - Fix read event on file for select/poll API

kernel - Fix read event on file for select/poll API

* select/poll have always returned an immediate read event on regular
  files, but kqueue is expected to only return a EVFILT_READ event
  when not sitting at the file EOF.

* The kernel adds a NOTE_OLDAPI flag which filter functions can use to
  discern between select/poll and kqueue related knotes.

* Adjust filesystem filter function to always return an immediate
  event for reads via select/poll.

* Fixes guile, which for some reason beyond our ken select()'s for a
  read event on a file.

Reported-by: Johannes Hofmann <johannes.hofmann@gmx.de>