Switch FSFS index API functions that could actually use two different pool
parameters to the two-pool paradigm.

Although almost all current callers will pass the same (temporary) pool to
both parameters, this patch improves consistency, readability and
documentation.

* subversion/libsvn_fs_fs/index.h
  (svn_fs_fs__p2l_index_lookup,
   svn_fs_fs__p2l_entry_lookup,
   svn_fs_fs__l2p_get_max_ids): Accept two pools instead of one.

* subversion/libsvn_fs_fs/index.c
  (p2l_index_lookup): The POOL parameter is actually a SCRATCH_POOL. All
                      results are flat data stored in the pre-allocated
                      *ENTRIES result.
  (svn_fs_fs__l2p_get_max_ids,
   svn_fs_fs__p2l_index_lookup): Only the result array needs to be allocated
                                 in the RESULT_POOL. It contains flat data
                                 and no pointers.
  (svn_fs_fs__p2l_entry_lookup): Use the SCRATCH_POOL with function calls
                                 only require a temporary pool.

* subversion/libsvn_fs_fs/cached_data.c
  (svn_fs_fs__check_rep,
   block_read): Update caller by passing the same pool to both parameters.
                That pool is already for temporaries only.

* subversion/libsvn_fs_fs/pack.c
  (pack_range,
   append_revision): Same.
  (pack_log_addressed): Update caller, actually providing different pools.

* subversion/libsvn_fs_fs/verify.c
  (compare_l2p_to_p2l_index): Same.
  (compare_p2l_to_l2p_index,
   compare_p2l_to_rev): Update caller by passing the same temporary pool
                        to both parameters.

* subversion/svnfsfs/dump-index-cmd.c
  (dump_index): Same.

* subversion/svnfsfs/stats-cmd.c
  (read_log_rev_or_packfile): Same.

git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1627497 13f79535-47bb-0310-9956-ffa450edef68