Recent concurrency improvements in the AHCI driver and CAM need testing

[Matthew Dillon]

:Hello, 
:
:this breaks USB (daX) disks for me. After all daX disks are initialized, it hangs after:
:
:da8 at umass-sim0 bus 0 target 0 lun 0
:da8: <WD Ext HDD 1021 2002> Fixed Direct Access SCSI-4 device 
:da8: Serial Number WMAVU2232228 
:da8: 40.000MB/s transfers
:da8: 1430797MB (2930272256 512 byte sectors: 255H 63S/T 182401C)

    Ok, I'm on it.  It's a degenerate condition somewhere for the case
    where the device is not NCQ.

						-Matt