Instead clear updates on the work-in-progress during the begin phase. Aborted updates are recovered by cloning from the current fiber.
This is needed to get the triangle demo working.
This builds a `react-dom-fiber.js` bundle which exposes ReactDOMFiber. This allows early experiments with the new Fiber reconciler. I also expose it in the npm package through `react-dom/fiber`.
Andrew Clark
Sebastian Markbåge
Sebastian Markbage