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)

Rename the generic "CLASS" to the more specific "GEOM_CLASS".
While I'm here remove redundancy and inconsistencies.

Obtained from: Juniper Networks

- Add a manual page for graid3(8) utility.
- Connect it to the build.
- Inform geom(8) about it.

Introduce GEOM RAID3 class, i.e. kernel module, which implements RAID3
transformation and graid3(8) userland utility, which can be used for
configuration. No manual page yet, sorry.

Hardware provided by: Daniel Seuffert