Currently if React is not loaded, ReactDOM shows this:

<img width="664" alt="screen shot 2017-08-08 at 3 36 52 pm" src="https://user-images.githubusercontent.com/810438/29077217-784c7624-7c4f-11e7-88bc-b055407523a9.png">

We should throw a nicer error message in the entry point I think.
render: ReactMount.render,
  unmountComponentAtNode: ReactMount.unmountComponentAtNode,
  version: ReactVersion,
  
  unstable_batchedUpdates: ReactGenericBatching.batchedUpdates,
  unstable_renderSubtreeIntoContainer: ReactMount.renderSubtreeIntoContainer,
  
  __SECRET_INTERNALS_DO_NOT_USE_OR_YOU_WILL_BE_FIRED: {
    
    EventPluginHub: require('EventPluginHub'),
    
    EventPluginRegistry: require('EventPluginRegistry'),
    EventPropagators: require('EventPropagators'),
    ReactControlledComponent: require('ReactControlledComponent'),
    ReactDOMComponentTree,
    ReactDOMEventListener: require('ReactDOMEventListener'),
    ReactUpdates: ReactUpdates,
  },
};
if (
  typeof __REACT_DEVTOOLS_GLOBAL_HOOK__ !== 'undefined' &&
  typeof __REACT_DEVTOOLS_GLOBAL_HOOK__.inject === 'function'
) {
  __REACT_DEVTOOLS_GLOBAL_HOOK__.inject({
    ComponentTree: {
      getClosestInstanceFromNode: ReactDOMComponentTree.getClosestInstanceFromNode,
      getNodeFromInstance: function(inst) {
        
        if (inst._renderedComponent) {
          inst = getHostComponentFromComposite(inst);