* Add a dkdevice; move sc_*openpart, sc_label, and sc_cpulabel into it.
* Turn sc_wlabel into a flag, and don't set it automatically in DIOCWLABEL.
* If there is no label, disallow all I/O except to the raw partition.
* Don't allow I/O to `unused' partitions.
* Beginnings of support for block sizes other than 512 bytes.
Other minor changes.