a signature file, rather it compares the actual data in the image file vs.
what is on a disk.  Mostly a debugging option, trying to find the source
of a disk corruption problem when loading images with FBSD 4.10.

Teach it about relocations, and (optionally) have it not compute hashes
for blocks which involve relocations, since those areas will likely always
differ in the image and disk.  The default behavior is to have it look at
everything as before, use -N to have it skip relocation areas.