title: Stable reactid for server-side rendering
body: <p>When using React to render components on the server, I notice that the data-reactid attributes are effectively random. I understand that's expected. (<a href="https://groups.google.com/forum/#!topic/reactjs/ewTN-WOP1w8">https://groups.google.com/forum/#!topic/reactjs/ewTN-WOP1w8</a>) </p>
  
  <p>However it's a little surprising that this otherwise functional framework introduces such non-determinism in the view output. It means that successive renderings of a view with identical state will create different HTML, preventing, for instance, the view engine from returning a '304 Not Modified' or generating a reliable ETag. (I appreciate such caching could be handled at a higher infrastructure layer as well.)</p>
  
  <p>Is there a way to seed the generation of the identifier so that the reactids are deterministic? Or is the reason that's a bad idea explained somewhere else?</p>