The error bubbles through the event processing loop, breaking it and
hanging the application.
Instead, there is now a .exception(e) method on XMLStream which may
be overridden or reassigned that will receive all unhandled exceptions
(read: not XMPPError) from event and stream handlers.
Now with dynamic node handling goodness.
Some things are not quite working yet, in particular:
set_items
set_info
set_identities
set_features
And still need more unit tests to round things out.
