Use "offset == 0" not "period == 0" to denote async trasnfers.
Implement TARG_IMMEDIATE_SCB non-disconnected target mode
SCB delivery scheme.
In our timeout handler, don't rely on the phase already being
set to denote an active connection. IDENTIFY_SEEN is more
than sufficient.
Verify that the softc passed in ahc_detach is still known
to the driver before blindly using it.