As per convention, sub-pools shall be named "subpool".

* subversion/libsvn_fs_base/fs.c
  (svn_fs_base__clean_logs): s/sub_pool/subpool/g.

* subversion/libsvn_fs_fs/cached_data.c
  (svn_fs_fs__rep_chain_length): Same.

* subversion/libsvn_fs_x/cached_data.c
  (svn_fs_x__rep_chain_length): Same.

* tools/dev/fsfs-access-map.c
  (open_file): Same.

git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1627502 13f79535-47bb-0310-9956-ffa450edef68