- make esp_poll() approximate the given timeout value.
- introduce esp_abort(), and use it for timed out commands; make targets and driver less confused.
- make {free,ready,nexus}-list management somewhat more coherent.
- make sure we only proceed down the state machine in espintr()
if there really is an interrupt pending.
get an "Illegal command" (why is this?) when we try to pull it in.
On detection of this condition, we reset the SCSI bus and simply stop asking
this target for an identify messages, for now.