Fixed the issue where the firstplay event wouldn't fire if the play even...

...t was fired before loadstart
I think there are still scenarios where the loadstart-play relationship is going to get messed up. For instance, loading a video initially and then replacing it before `play()`. That would produce two loadstarts and then a play, and would cause the `hasStarted` handler to get invoked twice. I don't think that particular order would cause errors but it could be confusing. I was proposing something more like this:

```js
/* in Player.init */
this.on('play', function() {
  if (!player.hasClass('vjs-has-started')) {
    player.addClass('vjs-has-started');
    player.trigger('firstplay');
  }
});
this.on('loadstart', function() {
  if (player.hasClass('vjs-has-started')) {
    player.removeClass('vjs-has-started');
  }
});
```