Simplify composite lifecycle state

We now forbid calling setState or forceUpdate if any component's render function is higher in the stack, not just the component you're trying to update. (We do this already now for React.renderComponent and React.unmountComponentAtNode.)

This also has the advantage that we can now remove CompositeLifeCycle.RECEIVING_STATE, making _compositeLifeCycleState easier to reason about (not to mention that RECEIVING_STATE was a confusing name), and removing a try/finally from the render path which might help with perf.