Stricter types for ndarray __getitem__ and __setitem__

[dmoisset]

Currently they accept anything. Being stricter needs some care because both accept setting and converting scalars, arrays, or python values, and they also can accept python objects, arrays, slices, etc as keys.

[dmoisset]

Documentation at http://docs.scipy.org/doc/numpy/reference/arrays.indexing.html#arrays-indexing