Bug in gl_space.py?

In gl_space.py I stumbled over the statement at https://gitlab.mpcdf.mpg.de/ift/NIFTy/blob/master/nifty/spaces/gl_space/gl_space.py#L164

  `  lat = qr_tuple[0]*(np.pi/(self.nlat-1)) `

It seems that the code assumes that the ring latitudes of the GL grid are equidistant ... which is definitely not the case.

However I'm wondering if the "get_distance_array" functionality is needed at all for spaces that do not live in the harmonic domain. If I understand correctly, this is only used for binning when producing a power spectrum. If this assumption is correct, I suggest to remove the "distance_array" related methods from GL and HP spaces. (This involves removing a few tests as well.) Maybe it would be good to make it explicit in the class hierarchy that this method is only supported by spaces which live in the harmonic domain.