I've added an extra check for the gradient ( I used to have it in my branch,
because I think at one point I got an error because of that, though I'm not
100% sure we should need to do that check).

Since the name gets into the C code, this would cause different modules
(with different C code) to have equal keys.

output is not differentiable.

Sorry guys, this copying things from one side to the other is harder then I
thought, but I think I figured out how to do it ;)

Lop is based on the grad methods that are already implemented, while Rop
requires rop methods for each op that are going to be pushed soon.

Also now print for each apply if c code where used.