All the mbr code now seems to be working. We can build a basic
unix disklabel in any existing DOS partition while retaining the
existing mbr bootcode or we can install to the whole disk which
puts FreeBSD's boot code into the MBR and creates a clean MBR
partition table with FreeBSD in partition 0 taking up the whole disk.
use dialog functions properly
move alloc_memory early to prevent core dump at stage 3
Change 25x80 to 24x80
Fix setenv diagnostic
Fix Fatal to call end_dialog()