MFC 254072:

MFC 254072:
Don't emit a spurious EVFILT_PROC event with no fflags set on process exit
if NOTE_EXIT is not being monitored.  The rationale is that a listener
should only get an event for exit() if they registered interest via
NOTE_EXIT.  This matches the behavior on OS X.
- Don't save the exit status on process exit unless NOTE_EXIT is being
  monitored.
- Add an internal EV_DROP flag that requests kqueue_scan() to free the
  knote without signalling it to userland and use this when a process
  exits but the fflags in the knote is zero.

git-svn-id: svn://svn.freebsd.org/base/stable/8@257760 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f