Hi,
I was receiving the same error with jboss-eap6.1 beta. After messing around with module dependencies, I copied myfaces-api-2.1.8.jar into my web-apps WEB-INF\lib, and now jsf.js can be found and all ajaxified pages are loading and working fine. I don't think that this is a good and permanent solution, but for me it was more important to get my app up and running.
Hope this helps