On the fsfs-format7 branch: Switch util (file name construction functions)
API and transaction.c internal usage of txn IDs from C string to struct.
Large parts of this patch trivially change the type of pass-through params.

Opportunistically update index.* and cached_data.c that simply pass the
txn_id parameter through to util.* .

This is the fifth larger patch in the "numerical IDs" patch series.

* subversion/libsvn_fs_fs/util.h
  (path_txn_dir,
   path_txn_changes,
   path_l2p_proto_index,
   path_p2l_proto_index,
   path_txn_props,
   path_txn_next_ids,
   path_txn_item_index,
   path_txn_proto_rev,
   path_txn_proto_rev_lock): switch txn_id parameter type to struct

* subversion/libsvn_fs_fs/util.c
  (combine_txn_id_string): new utility function
  (path_txn_dir): update; use new utility
  (path_txn_sha1): simplify
  (path_txn_changes,
   path_txn_props,
   path_l2p_proto_index,
   path_p2l_proto_index,
   path_txn_next_ids,
   path_txn_item_index): signature change only
  (path_txn_proto_rev,
   path_txn_proto_rev_lock): update; use new utility
  (path_txn_node_rev): simplify

* subversion/libsvn_fs_fs/cached_data.c
  (open_and_seek_transaction): drop parameter conversion

* subversion/libsvn_fs_fs/index.h
  (svn_fs_fs__item_offset): update pass-through parameter type

* subversion/libsvn_fs_fs/index.c
  (l2p_proto_index_lookup,
   svn_fs_fs__item_offset): ditto

* subversion/libsvn_fs_fs/fs.h
  (fs_fs_shared_txn_data_t): switch txn ID member to struct

* subversion/libsvn_fs_fs/transaction.c
  (get_shared_txn,
   free_shared_txn): update signature; simplify 
  (unlock_proto_rev_baton,
   get_writable_proto_rev_baton): switch txn_id member to struct
  (unlock_proto_rev_body,
   get_writable_proto_rev_body): update; convert txn ID to string for errors
  (unlock_proto_rev,
   unlock_proto_rev_list_locked,
   get_writable_proto_rev): update
  (purge_shared_txn_body,
   purge_shared_txn): switch txn_id pass-through type
  (svn_fs_fs__txn_changes_fetch): convert txn id to struct
  (svn_fs_fs__create_txn): update caller
  (get_txn_proplist): update signature
  (svn_fs_fs__change_txn_props,
   svn_fs_fs__get_txn): update caller
  (write_next_ids,
   read_next_ids, 
   get_new_txn_node_id): update signature
  (svn_fs_fs__reserve_copy_id,
  (svn_fs_fs__purge_txn): convert txn id to struct
  (svn_fs_fs__create_node,
   set_uniquifier): update caller
  (svn_fs_fs__add_change): convert txn id to struct
  (store_l2p_index_entry,
   store_p2l_index_entry,
   allocate_item_index): update signature
  (rep_write_cleanup,
   rep_write_contents_close): update caller
  (write_hash_rep,
   write_hash_delta_rep): update signature
  (write_final_rev): update caller
  (write_final_changed_path_info): change signature; update
  (write_final_current): change signature
  (verify_locks): change signature; update
  (commit_body,
   svn_fs_fs__open_txn,
   svn_fs_fs__txn_proplist): update caller


git-svn-id: https://svn.apache.org/repos/asf/subversion/branches/fsfs-format7@1454950 13f79535-47bb-0310-9956-ffa450edef68