Warning of unhandled iopub "data_message" in hub.save_iopub_message()

[rjplevin]

engine.datapub.publish_data() sends a "data_message", but this isn't recognized in hub.save_iopub_message(). Is this expected behavior? It produces only a warning, but it leaves me wondering if there's been a name change to "data_pub", which is handled.

[minrk]

I think the Hub should probably recognize the name and drop the message without a warning.