Enhance fsfs-access-map tool output by counting empty reads (at eof)
and unnecessary seeks as well.

* tools/dev/fsfs-access-map.c
  (file_stats_t,
   handle_info_t): add counters
  (store_read_info,
   read_file): update counters
  (seek_file): update init code
  (print_stats): show results

git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1523441 13f79535-47bb-0310-9956-ffa450edef68