Slice 0 is now for the first BSD slice. The first BSD slice is
the first DOSpartition with id 0xa5 or the whole disk if their
are no DOSpartitions (except the latter is not yet implemented).
Existing partitions on it work the same as in 2.0 except the
'd' partition is no longer special and partitions are relative
to the skice.
Slice 1 is now for the whole disk and gets a read-only label
describing the disk. Previously, slice 0 was for the whole disk
and there was no label on it.
Slices 2-31 are for DOSpartitions. Slice 0 is an alias for one
of these if there is a BSD slice. Previously, slices 1-31 were
for DOSpartitions.
diskslice_machdep.c:
Expand whole disk slice to include all DOSpartitions. More work
is required for >1024 cylinders and to rewrite the label iff the
driver is unsure about the geometry.
subr_diskslice.c:
New function dsisopen() to help handle media changes.
