controls with the section for the other MBR-using platforms that
already enable this)
* Don't prompt the user to "erase the previous contents of the disk"
when there's no NetBSD MBR partition; SAVEBOOTAREA is sufficient.
These fixes mean that you can create a disklabel (on an i386/amd64) on a disk
that doesn't have a NetBSD MBR partition without trashing the existing MBR.
The previous behaviour was extremely annoying when working with media such
as FAT-formatted CF cards, and didn't really protect people with such from
accidentally trashing part of sector 1 of such disks, and made it extremely
easy to trash sectors 0..15 of those disks instead.