[WIP] Recursion limit

Don't merge yet.

This advance gh-689. It flatten the Composite ops.

    This help gh-689 as it allow it to support up to 57 iteration of the
    loop instead of just 43.
    
    This could also help Theano cache in the case where graph could have
    different fusion order, so different way the composite are in each
    other, but do the same computation.
    
    This make the printing of Composite more readable.

It fail at 57 as we have a graph of add node instead of making one add with many inputs. I don't want to merge this now, as this will re trigger much compilation and as I'm working already on that, I'll try to tackle that too.