On the fsx-id branch:  In our noderev struct, use our internal ID part type
instead of the FS API ID to represent predecessor IDs.  Construct the FS API
level object on demand.

* subversion/libsvn_fs_x/fs.h
  (node_revision_t): Predecessor-ID has now the same type as the noderev-ID.

* subversion/libsvn_fs_x/low_level.c
  (svn_fs_x__read_noderev,
   svn_fs_x__write_noderev): Update parser / writer.  Take into account that
                             "unused" predecessor IDs are no longer simply
                             indicated by a NULL pointer.

* subversion/libsvn_fs_x/temp_serializer.c
  (svn_fs_x__noderev_serialize,
   svn_fs_x__noderev_deserialize): One sub-structure less to (de-)serialize.

* subversion/libsvn_fs_x/noderevs.c
  (svn_fs_x__noderevs_add,
   svn_fs_x__noderevs_get,
   svn_fs_x__noderevs_get_func): Predecessor IDs can now be read / set like
                                 any other ID part.  No temporaries needed.

* subversion/libsvn_fs_x/transaction.c
  (create_new_txn_noderev_from_rev): Update assignment.
  (svn_fs_x__get_txn): Construct the base ID on demand.
  (shards_spanned,
   choose_delta_base): Contents of the predecessor ID is now directly
                       accessible.

* subversion/libsvn_fs_x/dag.h
  (svn_fs_x__dag_get_predecessor_id): Since we will now construct the ID
                                      here, we need a result pool.

* subversion/libsvn_fs_x/dag.c
  (copy_node_revision): One sub-struct less to copy.
  (svn_fs_x__dag_get_node): Matching types simplifies assigment.
  (svn_fs_x__dag_get_predecessor_id): Construct the FS API level ID here.
  (make_entry): The NULL value is no longer the default for predecessor IDs.
                ID parts must be reset manually.
  (svn_fs_x__dag_clone_child,
   svn_fs_x__dag_copy,
   svn_fs_x__dag_update_ancestry): Update assignments.

* subversion/libsvn_fs_x/tree.c
  (x_closest_copy,
   history_prev,
   verify_node,
   svn_fs_x__verify_root): Update svn_fs_x__dag_get_predecessor_id callers.

git-svn-id: https://svn.apache.org/repos/asf/subversion/branches/fsx-id@1647111 13f79535-47bb-0310-9956-ffa450edef68