Flow.reloading() should modify the flow in-place

[jqmp]

Right now, when you call Flow.reloading(), you get a new copy of the flow with reloaded state. I think it should also mutate the flow to use the new state.

The current behavior is consistent with the other flow methods, which also return new copies rather than modifying the original flow. However, in this case I think the user will pretty much always want the new state, and I often get caught using an out-of-date version of the flow by accident. Since reloading is already a global, magical operation, I'm okay with being a little inconsistent here.