[CAM] Widening lun_id_t to 64-bits

Modern SCSI hardware often uses 64-bit logical units (LUNs). The patch 
found at http://people.freebsd.org/~nwhitehorn/lun64.diff widens the 
type of lun_id_t to 64 bits, bumps CAM_VERSION, and begins exposing 
these to drivers that are marked as supporting extended LUNs. No 
behavior is changed except that peripheral with very long LUNs that 
didn't work before will start working. Binary compatibility with old 
code is also kept. There is, however, a chance that some 3rd party 
software might be unhappy about the type widening, so I'd appreciate any 
testing results. Barring any issues, I will commit this on Friday.
-Nathan