SE-0472: Starting tasks synchronously from caller context

[pyrtsa (Pyry Jahkola)]

@ktoso

Task.immediate or Task.startImmediately - actually sound interesting... I wonder if "immediate task" isn't a bad way to describe this, it starts immediately after all, and if it has to it'll hop somewhere

I suggested Task.immediate in the pitch thread, and still think it'd be the best name for this.