Copy stable/9 to releng/9.3 as part of the 9.3-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Copy head to stable/9 as part of 9.0-RELEASE release cycle.

Approved by: re (implicit)

Spelling fixes.

mdoc: order prologue macros consistently by Dd/Dt/Os

Although groff_mdoc(7) gives another impression, this is the ordering
most widely used and also required by mdocml/mandoc.

Reviewed by: ru
Approved by: philip, ed (mentors)

Note that the structures are defined in <sys/user.h> in the text (using
language from stat(2)) rather than in the synopsis.

Requested by: bde

- Note that these interfaces require <sys/user.h> for the structure
definitions.
- Note that these functions return NULL on failure.

MFC after: 3 days

Add filler man pages for the kinfo functions I added recently.
While here, hook up the hexdump(3) man page which wasn't being installed.