Added support for the Apple High Speed SCSI card.

Added support for the Apple High Speed SCSI card.

This means that you can now connect hard drive images to the emulator,
and, with the addition of the AHSSC emulation, connect up to seven of
them to one system (technically, with 8 LUNs per SCSI ID, you could in
theory connect 56 of them, but that's just crazy).  The emulation of
the card is still in an early state, but it currently seems to work
properly with the "Pitch Dark" hard drive image by 4am.  Still needs
some work to expose it properly to the GUI, but hey, that's just
details.  :-)