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.
Re-organised files, moved bootcode routines into their own files.
Check return types of everything and pass error messages to
windows so we get good diagnostics.
Made start on stage 2 installation. Implemented a status file that
keeeps track of where we are in the installation process and allows
installation from media sequences.
