Switch FSFS' create_rep_state() function to the dual-pool paradigm.
Make some callers pass a scratch pool to reduce memory overhead.

* subversion/libsvn_fs_fs/cached_data.c
  (create_rep_state_body, create_rep_state): Switch to dual-pool and
   use a scratch pool for data not returned to the caller.
  (svn_fs_fs__check_rep, svn_fs_fs__get_file_delta_stream): Pass the
   standard pool as scratch pool.
  (svn_fs_fs__rep_chain_length, build_rep_list): Use an iterpool during
   loops and pass it as scratch pool to create_rep_state().


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1604824 13f79535-47bb-0310-9956-ffa450edef68