Stub object throw an exception after comparsion

[grapemix]

I have set up a stub object and assign a fxn as property. But when other part of the code try to compare the stub object with some given atomic value, ludibrio will try to call the given atomic value, and hence the stub object will throw an exception because the atomic value from the external library code is not callable. I fork ludibrio and fixed it, please pull. Thanks.

https://github.com/grapemix/ludibrio