hammer - Collect record statistics, implement ^T and ^C

hammer - Collect record statistics, implement ^T and ^C

* Add a check for ^C

* Add a check for ^T and print statistics.

* When doing the dedup for real run a pre-pass on the b-tree to count the
  number of data records present so the ^T feature can print out progress.

  This also has the side effect of doing locality-of-reference disk
  accesses to allow the b-tree data blocks to be cached by the kernel
  (or swapcache) before doing the real pass which will insert random data
  block reads when verifying duplicates.  Due to the efficiencies both passes
  should run faster than the original combined pass, or at least not take
  too much longer.