ext_dir that is absolute directory name of where files are located to
extract. All setup routines must set that directory name correctly.
Make target.c compile if DEBUG is set.
and current-root-is-target-root (pmax diskimage.
* Add code to check disk names (e.g., "sd0") against the current
kern.root_device sysctl (whic does *not* include a partition).
* Add new function must_mount_root():
check to see if it's the same device as the root. If not,
the current and target root partitions cannot overlap.
If they do, do statfs() on "/", and return 1 iff we get back
"root_device" as the mounted-on filesystem, otherwise zero.
* Call must_mount_root() right after the user specifies a disk as
install/upgrade target, and if it returns 1, print a message asking
them to mount root, and abort.
* Use statfs("/") mounted_from string to check if a disk partition
(e.g., "sd0a") matches the current root.
perry