BUG: cluster: _vq should check whether dtypes are same or not
BUG: cluster: _vq unable to handle large features

_vq.vq should initialize outdists to INF but ndarray.fill seems
to treat NPY_INFINITY as an int32 and initialize outdists
as 2 ^ 31 - 1, so that the result may be wrong when the features
are large. Use np.inf to fill outdists would be safer.