creation of distributed_data_object without dtype

In rg_space.py and power_space.py there are calls to the constructor of "distributed_data_object", which do not specify a "dtype" argument. This is accepted by D2O, but an annoying message is printed to the console. I would suggest to produce a hard error whenever the user tries to create a D2O object without specifying a type. However, for the time being: is it correct to specify "dtype=np.float64" in the two cases I mentioned?

A related question: inside the distance_array-related functions of RGSpace and LMSpace, the data type np.float128 is used. Is that deliberate or an oversight?