2 small fixes: in NdArrayResolver and changeAttrExpression

Maybe it is also a good idea to add in DefaultResolver some logic for additional dictionary values evaluation in case of class has '\_\_getitem\_\_' method. 
I think the problem is that numpy is probably only returning views (and probably creates a new one on each call to the subarray -- the fact that the ids match at any chance is probably always random -- we get lucky sometimes that the python allocator tries to reuse PyObject ids)... if that's the case, the DictResolver probably won't work (in this case the solution would be really creating a custom wrapper class for it and a custom resolver).