debug - Add seekbench.c

debug - Add seekbench.c

* Add a little program which purposefully attempts to defeat OS and disk
  caches to calculate seek latencies for different relative seek spans.

  Well, this doesn't tell us anything we didn't know already, that being
  that unless one can make accesses use of the HDs zone cache well anything
  other than a linear read is going to have a fairly huge seek-time cost.