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.
const hostContextDev = ((hostContext: any): HostContextDev);
      if (
        typeof newProps.children !== typeof oldProps.children &&
        (typeof newProps.children === 'string' ||
          typeof newProps.children === 'number')
      ) {
        const string = '' + newProps.children;
        const ownAncestorInfo = updatedAncestorInfo(
          hostContextDev.ancestorInfo,
          type,
          null,
        );
        validateDOMNesting(null, string, null, ownAncestorInfo);
      }
    }
    return diffProperties(
      domElement,
      type,
      oldProps,
      newProps,