Remove $MBR special file from XTAF

Xbox disks don't have an "MBR."  The first sector is blank, there is no
partition table, and the disk has no standard area to store a
bootloader.

(In the future, two special files of the disk may be considered, to
represent the contents at disk offsets 0x800 and 0x2000.)

This addresses:
<https://github.com/ajnelson/sleuthkit/issues/6>

Signed-off-by: Alex Nelson <ajnelson@cs.ucsc.edu>
Add newline to debug statement
Update XTAF VS debug prints
Creating XTAF volumes: Add labels and success checks

This fixes:
<https://github.com/ajnelson/sleuthkit/issues/7>

Signed-off-by: Alex Nelson <ajnelson@cs.ucsc.edu>