about-to-show callback to better handle having a NULL callback, and thus NULL data. Putting some protections in as well so we'll get better errors from it if we make this mistake again.
that hud-service sends.
This change takes all of the events on a client and puts them into single dbus messages to be sent to the server. It also does the same thing for about-to-show messages. Both sets of messages are reserialized on either side to make callers unable to notice the difference.