be probed several times. This fixes the "ATAPI CD probed as wd drive" problem.
Thanks to Geoff Wing <mason@primenet.com.au> for testing this on his hardware.
(currently only CD-ROM drives on i386). The sys/dev/scsipi system provides 2
busses to which devices can attach (scsibus and atapibus). This needed to
change some include files and structure names in the low level scsi drivers.