Used relationship name in the naming of creation methods for has_one

@seancarr 

Tested in db_schemas. Only affects 2 classes and effected methods in these classes weren't being used.

I'm not entirely satisfied with this solution. Would prefer to change some members in AssociationDefn, but I don't know the full implications of such changes. This change is small, simple, and gets us the desired behavior.
Think you're referring to the member assoc_model_name in AssociationDefn. That value is just the class name, not the relationship name. Currently, there is nothing in AssociationDefn that has the relationship name.

I'd preferrer changing assoc_model_name to the relationship name (instead of placing this logic in the template), but that might break stuff in other places that use AssociationDefn.assoc_model_name.