sector granularity for both offset and length. Have all schemes use mkimg_write() instead of mkimg_seek() followed by write(2). Now that schemes don't use lseek(2) nor write(2) directly, it's easier to support output formats other than raw disks.
<sys/diskmbr.h> and not the unique defines introduced later.
The partitioning scheme can be one of the schemes supported by gpart. Reviewed by: sjg Obtained from: Juniper Networks, Inc.