machine-independent code and try mounting the devices in the
lists instead of guessing alternative root devices in a machine-
dependent way.
autoconf.c:
Reject preposterous slice numbers instead of silently converting
them to COMPATIBILITY_SLICE.
Don't forget to force slice = COMPATIBILITY_SLICE in the floppy
device name.
Eliminated most magic numbers and magic device names in setroot().
Fixed dozens of style bugs.
vfs_conf.c:
Put the actual root device name instead of "root_device" in the
mount struct if the actual name is available. This is useful after
booting with -s. If it were set in all cases then it could be used
to do mount(8)'s ROOTSLICE_HUNT and fsck(8)'s hotroot guess better.