ResteasyProviderFactory not cleaned up on undeploy.

When RESTEasy jars are deployed in a shared environment (i.e. deployed in AS classpath), ResteasyProviderFactory is not released on undeployed causing a non-trivial graph of references to be leaked. The static field in RuntimeDelegate should be cleared.

The problem is that RuntimeDelegate caches the provider factory in a static field. On undeploy, the field should be cleared (if it had not been replaced by another deployment's provider factory in the meantime)

Reference graph:

javax.ws.rs.RuntimeDelegate -> ThreadLocalResteasyProviderFactory -> ResteasyProviderFactory