ids are always set to null

[Matt]

This might be related to (and/or fixed by) # 456441 [1], but ids don't seem to be echoed back to the caller per the specification [2].

% twistd --python id_test.py # attached to this bug report
% curl 'http://127.0.0.1:6969/' -H 'Content-Type: application/json' -H 'Accept: application/json' -X POST --data '{ "method": "hello", "params": ["Duncan"], "id": 101}'
{"id": null, "result": "Hello, Duncan!", "error": null}

Note that id 101 was passed in the call, but null was returned.

[1] https://bugs.launchpad.net/txjsonrpc/+bug/456441
[2] http://json-rpc.org/wiki/specification