On the fsx-id branch:  Switch txn commit code over to our internal ID type.

* subversion/libsvn_fs_x/transaction.c
  (validate_root_noderev): Directly construct the needed noderev-ID.
  (write_final_rev): Switch the returned ID to our internal type. 
  (commit_body): Update caller.

git-svn-id: https://svn.apache.org/repos/asf/subversion/branches/fsx-id@1647757 13f79535-47bb-0310-9956-ffa450edef68