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
ext2fs: Return EINVAL for negative uio_offset as in UFS.

While here drop old comment that doesn't really apply.

MFC after:	1 month
Discussed with:	gleb
sh: Remove #define MKINIT.

MKINIT only served for the removed mkinit. Many variables can be static now.