numpy random functions do not trigger array interface

[mocquin]

An related issue is opened at numpy : numpy/numpy#19382 (and also mentionned in numpy/numpy#18902 (comment))

In the case of physipy:

import numpy as np
from physipy import m

# raises a DimensionError, by trying to convert to float
np.random.normal(loc=0.5*m)

# it is not a matter that loc and scale must have same dimension since
# the following also fails
np.random.normal(loc=0.5*m, scale=0.5*m)