Improve isolation between integration code and user code

It is currently possible for user code to "see" some JBossWS integration classes & dependencies during the execution of static blocks of user handlers declared through webservices.xml descriptors or management model. That happens because such code is executed at deployment time when the JBossWS integration classloader is set as thread context classloader. We should prevent this from happening.
This is not a problem, of course, at runtime, when the deployment is completely isolated from the integration classloader.