On the fsx-id branch: Simplify node_revision_t duplication code before
we add more members to it.

* subversion/libsvn_fs_x/dag.c
  (copy_node_revision): Use duplicating allocation to create the copy.
                        Also, make it a deep copy of *all* elements.
  (svn_fs_x__dag_dup,
   svn_fs_x__dag_copy): Simplify caller.

git-svn-id: https://svn.apache.org/repos/asf/subversion/branches/fsx-id@1645894 13f79535-47bb-0310-9956-ffa450edef68