* The diskslice abstraction now stores offsets/sizes as 64 bit quantities.

* The diskslice abstraction now stores offsets/sizes as 64 bit quantities.
  (NOTE: DOS partition tables and standard disklabels can't handle 64 bit
  sector numbers yet).  For future pluggable disklabel/partitioning schemes.

* The kernel panic / kernel core API is now 64 bits.

* The VN device now uses 64 bit sector numbers and can handle block devices
  up to what is supported by the filesystem (typically 8TB).  This change
  was made primarily so we can test future disklabel / partition table
  support.

* Pass 64 bit LBAs to various block devices and to the SCSI layer.

* Check for and assert 32 bit overflow conditions in various places, instead
  of wrapping.