this patch implements the new command allocation scheme for SCSI
Core, using the slab cache and a free_list for each host for a
backup store of one command (or many).

 o The three (3) subversion means that it has been updated to use
   ISA DMA and PCI DMA memory for scsi command allocation,
   i.e. there's two scsi command caches now.

 o The interface is, of course, unchanged; and this is the whole
   point of making this allocation scheme -- i.e. the allocator
   is abstracted.