On the fsx-id branch:  Use noderev IDs to read noderevs at the
caching layer.  Update sub-functions and callers.

* subversion/libsvn_fs_x/cached_data.h
  (svn_fs_x__get_node_revision): Switch ID type.

* subversion/libsvn_fs_x/cached_data.c
  (err_dangling_id,
   get_node_revision_body, 
   svn_fs_x__get_node_revision): Switch ID parameter type and update
                                 implementation.
  (svn_fs_x__get_mergeinfo_count): Update caller.

* subversion/libsvn_fs_x/dag.c
  (get_node_revision): Same.

* subversion/libsvn_fs_x/transaction.c
  (create_new_txn_noderev_from_rev,
   svn_fs_x__get_txn, 
   shards_spanned,
   choose_delta_base,
   validate_root_noderev,
   write_final_rev,
   svn_fs_x__delete_node_revision): Same.

* subversion/libsvn_fs_x/tree.c
  (merge): Same.

git-svn-id: https://svn.apache.org/repos/asf/subversion/branches/fsx-id@1645609 13f79535-47bb-0310-9956-ffa450edef68