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

__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.

better test for the canonizer. skip test that are know to fail because they are not implemented. They are not real error or failure.

changed CLinker.cmodule_key to do the real computation in a static method to allow calling it from elsewhere.