add_relationship & input == ouput for add_entity

[tmsincomb]

The only thing that sometimes doesn't match the input for add_entity is the superclass ilx_id is forced to have it complete url form for output for convenience down the line.

[tgbugs]

Thanks for pulling this together. One comment. It is almost never correct to use sys.exit in a python library, if you need to 'exit' early you should raise an exception.