o Detect when Boot Camp is enabled (i.e. the MBR mirrors the GPT).
o When Boot Camp is enabled, update the MBR whenever we write the GPT.
o Creation of a Boot Camp enabled GPT is not supported.
o Automatically disable Boot Camp when the GPT has been changed so that
there's either no EFI partition or no HFS+ partition.
o The first 4 partitions (by index) get mirrored in the MBR.
Requested by, discussed with and tested by: kris@pcbsd.org
MFC after: 1 week