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

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

- change "is is" to "is" or "it is"
- change "the the" to "the"

Approved by: lstewart
Approved by: sahil (mentor)
MFC after: 3 days

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