Enhance the description of NOTE_TRACK:

• NOTE_TRACK has never triggered a NOTE_TRACK event from the parent pid. If NOTE_FORK is set, the listener will get a NOTE_FORK event from the parent pid, but not a separate NOTE_TRACK event.
• Explicitly note that the event added to monitor the child process preserves the fflags from the original event.
• Move the description of NOTE_TRACKERR under NOTE_TRACK as it is not a bit for the user to set (which is what this list pupports to be). Also, explicitly note that if an error occurs, the NOTE_CHILD event will not be generated.

MFC after: 1 week