kernel - implement serialno for kqueue poll handling part 1/2

kernel - implement serialno for kqueue poll handling part 1/2

* The kqueue implementation for the poll system call was improperly
  triggering on spurious events.

* Adjust the poll support code to implement a serial number scheme
  similar to how the select code works.  The poll array index is also
  encoded.

* poll() handles unsupported POLLPRI and POLLRDBAND requests differently
  from select().  poll() ignores these requests if they are not supported
  (select returns an error).

  Allow kqfilter functions to return EPERM or EOPNOTSUPP to indicate
  an unsupported filter.  Return values will be fixed in part 2.