On the fsfs-format7 branch:  Implement layout optimizing fsfs packing
for format7 repos.  Code works but still needs documentation and cleanup.

* subversion/libsvn_fs_fs/pack.c
  (rep_info_t,
   pack_context_t): new data types
  (initialize_pack_context,
   reset_pack_context,
   close_pack_context,
   copy_file_data,
   copy_item_to_temp,
   get_item_array_index,
   add_item_rep_mapping,
   copy_rep_to_temp,
   compare_dir_entries,
   copy_node_to_temp,
   compare_p2l_info,
   sort_items,
   compare_p2l_info_rev,
   sort_by_rev,
   pick_recursively,
   sort_reps,
   copy_items_from_temp,
   append_entries,
   write_l2p_index,
   pack_section,
   append_revision): various new utility functions
  (pack_log_addressed): new main pack function for format7 repos
  (pack_phys_addressed): new main pack function for format6 repos
   factored out from pack_rev_shared
  (copy_indexes): drop obsolete function
  (pack_rev_shard): simplify; call the suitable pack sub-function
  (pack_shard): provide extra parameter


git-svn-id: https://svn.apache.org/repos/asf/subversion/branches/fsfs-format7@1438453 13f79535-47bb-0310-9956-ffa450edef68