MFC r313436,r313437,r313438,r314587,r315687:

r313436:

Clarify #includes for hexdump(3) vs sbuf_hexdump(9)

hexdump(3) only requires libutil.h, whereas sbuf_hexdump(9) requires
sys/types.h (for ssize_t) and sys/sbuf.h

r313437:

Create link from hexdump(3) to sbuf_hexdump(9) as the manpage describes
sbuf_hexdump(9)'s behavior

r313438:

Clean up trailing and leading whitespace for variables to make it
consistent with the rest of the file and style.Makefile(9) a bit
more

r314587:

Correct MLINKS for sbuf_hexdump(9)

sbuf_hexdump(9) should be linked to sbuf(9), not hexdump(3). Another
review will be posted to deduplicate the sbuf_hexdump reference in
in hexdump(3) or at the very least make the information less duplicative.

r315687:

Document sbuf_hexdump(9) in just sbuf(9)

• Remove duplicate references to sbuf_hexdump(9) from hexdump(3). sbuf_hexdump(9) already pointed back to hexdump(3) for implementation details.
• Refer to sbuf_hexdump(9) instead of sbuf(9) for completeness