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)

Added PC-98 HDD boot manager. The boot0 is the `IPL' which occupies
sector 0 of a disk and boot0.5 is the `boot selector' which starts
from address 0x400. The IPL loads boot0.5 and boot0.5 loads bootblock
of a slice.

The boot manager stuff was developed by me (kato) with Borland C++,
and then, translated into bcc in the ports collection by Nokubi-san.
After that, boot0 has been translated into gas with the .code16
directive by Takahashi-san (nyan) and boot0.5 has been rewritten in
gas by me.