Support Etag mwEmbedLoader

@ranyefet looks like the Etag support was missing for mwEmbedLoader / AutoEmbed:

```bash
curl -I "http://kgit.html5video.org/tags/v2.0.2.rc4/mwEmbedLoader.php/wid/_243342/uiconf_id/12905712/entry_id/0_uka1msg4/playerId/1351566600?autoembed=true"
HTTP/1.1 200 OK
Date: Thu, 28 Nov 2013 18:56:58 GMT
Server: Apache/2.2.25 (Amazon)
X-Powered-By: PHP/5.3.27
Cache-Control: private, max-age=60
Expires: Thu, 28 Nov 2013 18:57:58 GMT
Connection: close
Content-Type: text/javascript
```

fixed in this pull request: 

Note both Etags hurt because of a 60 second ( or less? ) expire on server side generated KS. 

We should see about bumping that to a more reasonable amount of time like 24 hours like the default KS expire in startWidgetSession in the client lib.