Fix more encoding issues

Don't ask me exactly why this works, because I don't know. But my vague explanation is that the receiver method `AddUpdate()` expects an interface (i.e. a non-concrete type), but was getting a `JoinRequest`, which is a concrete type. So you have to explicitly declare `j` as an `Update` before sending it. Also you have to take its address; I think that has something to do with "settability." Reflection is weird.

The bootstrapping process runs now, but new siblings kick each other after the first compile. I'll leave that to you.