This is how I got it working for Jetty 9, and it should be basically the same for Jetty 8.
http://www.eclipse.org/jetty/documentation/current/framework-weld.html
It is easier to have the weld jar outside of the webapp as then you don't have to mess with tweaking the classes exposed to the webapp classloader like you are here (with the -org.eclipse.jetty bit for the ServletContext). I suspect there are more classes that would have to be added to that in order to make it work. You should get a note in the logging that says it is all enabled and active though.