Exported method parameters need to support dict types

[Ian Booth]

There is no dict marshaller. Therefore, although it is possible to declare that exported method parameters can be of type dict, it does not work in practice.

eg

    @export_write_operation()
    @operation_parameters(
        dict_param=Dict(
            key_type=xxxxxx,
            value_type=yyyyyy))
    @operation_for_version('devel')
    def someMethod(dict_param):