nomdl: can't round-trip ref types

	noms := types.NewValueStore((&chunks.TestStorage{}).NewView())
	emptyBlob := noms.WriteValue(types.NewEmptyBlob(noms))
	foo := types.NewStruct("", types.StructData{"b": emptyBlob})
	s := types.EncodedValue(foo)
	fmt.Println(s) // Prints: struct {b: #2eulo8v8rihcjm0e93brv14dopakkder}
	v := nomdl.MustParse(noms, s)
	fmt.Println(types.EncodedValue(v))