Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

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

Change the way powerpc bootable CDs are generated to work around a bug
in hybrid image generation in cdrtools. This produces a small HFS partition
containing loader, mapped in by an oddly-formed APM table using a new
feature in makefs. This does not appear to work yet on early-model G3
systems, which will be fixed later, but produces bootable CDs on
everything else.

Add a simple HFS boot block implementation for booting PowerPC macs. It creates
a small HFS filesystem with a CHRP boot script and an early-stage bootloader
derived from the sparc64 boot block.

Obtained from: sparc64