In the FSFS cached-data internal API layer, rename pools to the
scratch pools that they are.  No functional change.

* subversion/libsvn_fs_fs/cached_data.h
  (svn_fs_fs__check_rep,
   svn_fs_fs__rep_chain_length): Update signature.

* subversion/libsvn_fs_fs/cached_data.c
  (svn_fs_fs__check_rep,
   svn_fs_fs__rep_chain_length): Update implementation.

git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1605197 13f79535-47bb-0310-9956-ffa450edef68