Sorry for my delay in replying. I had the Final release to get out the door.
So the issue here is that by having hibernate in ear/lib it's always added to all deployments in the ear. What I would recommend you doing is moving it and xpto.jar to the war WEB-INF/lib since you mention that it is only used there. Due to the fact that we auto add hibernate with the presence of JPA annotations to all subdeployments (something I want to limit in a future release), you also need to add an exclusion for your war to not import the server's version of hibernate.
You do that by putting a jboss-deployment-structure.xml file in your ear's META-INF directory. There you list a <sub-deployment name="web.war"> and in that you add an <exclusions> with a module name of "org.hibernate".
Take a look at for more info and an example