in scalar.basic.Composte, fix the check that the scalar op implement the c_code. It was not working for Abs.

added OutputGuard sanity check to AddDestroyHandler to ensure that outputs are protected from destructive operations

implemented the c_code for the scalar mod op. It correctly implement the python semantic of mod on x86.

__hash__ functions are broken.

subject of where (if anywhere) these options should go.

better implementation of scalar.Composite.__eq__ and .__hash__. started the implementation of Composite pickling(disabled).

code change in softmax: removed the isinf and 0.0 checks because they would fail incorrectly for NaN inputs.

In a finished commit, the shape would replace the broadcastable parameter, since
the broadcastable vector can be computed from the shape.  The shape has None in
components that are unknown.

added scalar.Composite.__str__ as we don't want all element of the op to happear in the str representation.