On the fsfs-format7 branch: teach fsfs-access-map about index files

* tools/dev/fsfs-access-map.c
  (open_file): don't make index files appear as rev / pack files

git-svn-id: https://svn.apache.org/repos/asf/subversion/branches/fsfs-format7@1444693 13f79535-47bb-0310-9956-ffa450edef68