PropertyColumns of the same type are not treated as compatible for set expressions like Union

If you've got two PropertyColumns of the identical text type on different tables and if I am trying to do a Union over them, Storm will fail inside FindSpec.is_compatible method.

I am not sure what the best way to do this is, but I've gotten what I think should be the solution by getting the actual variable type and then comparing types. Branch attached to show what I mean.