1. Did not compute Linux free sectors correctly when superblock "first    data block" field was non-zero.  This happened with the Intel-provided    Dell boxen and their initial Linux disk.
1. Did not compute Linux free sectors correctly when superblock "first
   data block" field was non-zero.  This happened with the Intel-provided
   Dell boxen and their initial Linux disk.

2. Added some more sanity checks in the Linux code.

3. Fixed a bug I just introduced where slice mode would fail on a disk
   with an extended partition.

nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome