CS-PPC SCSI/CS-Mk3 SCSI change

[Ignatios Souvatzis <is%jocelyn.rhein.de@localhost>]

Hello,

I implemented code to detect when the SCSI host is completely unterminated
and to ignore it in this case.

Else NetBSD would hang as soon as it tried to use the Mk3/PPC scsi bus.
This was reported by Matthias Scheler. A similar fix was suggested by
Ralph Schmidt.

Just thought I shoudl let you know that the project hasn't died.

Regards,
        Ignatios