Figure out and implement task lifetime rules.

[eholk]

Originally tasks were going to be lexically scoped, so they die as soon as the task variable goes out of scope on the parent task. This is counter-intuitive to a lot of people, so we might have a list of child tasks and refer to them by handles instead. This also would let us reparent tasks when the parent dies before its children.

[pcwalton]

Is this completed now with tasks-as-ids?

[eholk]

There's a life cycle that's implemented, but I think the issue is more making sure it's a sane design. I'm not really sure what the status of the task tree is, or even if we still want it. We also don't have any sort of reparenting, and it's not possible to kill tasks.

[brson]

Let's make sure that failure propagation to parents works correctly, then maybe we can call this resolved.