multinomial newbackend

Fix test problem uncovered by test clean up (we where changed c_thunk=True globally, as we didn't do a deepcopy).

Norm

Function copy

Replace subtensors on broadcastable dimensions with DimShuffle

Make stack trace tests in `tensor/tests/test_opt.py` use `check_stack_trace`.

Use the normal way of getting a test. I think we should refactor the code to have a get_default_mode_c() method or give a parameter to get_default_mode(c=False).