xsdspec.AttributeGroupReference uses undefined function "get_type" in `to_python` method

[funkybob]

[FelixSchwarz]

Congrats - you managed to find some functionality which never worked. I followed the commits back to ec1e096 (the initial commit of this repo).

We have some get_type() helper in soapfish/utils.py which might part of the solution. Due to time constraints I can't look into the actual XSD specification for AttributeGroupReference so I'm not sure what should be returned by the to_python() method and how to implement that.

A good first step would be to add a test triggering the bug.