same for floppies (from Christoph Badura)
* allow user to run 'Configure network' multiple times, to correct errors
for example.
* deal with network interfaces that need explicit media type selection
(i.e. ask for it when it is needed, also store it in the generated
/etc/ifconfig.blah file on the destination disk)
* Add mount_with_unwind() that adds mountpoint to a LIFO queue
of mountpoints to undo on error. Use in target_mount().
* Add unwind_mounts() which traverses the LIFO queue and unmounts
filesystems, silently ignoring errors.
* create toplevel() function which displays banner message and
calls unwind_mounts().
* change toplevel menu to call toplevel() instead of inline banner.
Where to do unwinds needs more thought. Perhaps we should only unwind
if an upgrade or install appears unsuccessful, so after a successful
install, the target is mounted (e.g., for upgrading /etc/rc.conf).
bouyer