public void stop() {
        registration.unregister();
        registration = null;
    }
A bundle {@link CollisionHook} that contains a set of bundles that are allowed to collide with bundles
that are about to be installed. This class also implements a {@link FindHook} to provide a consistent
view of bundles such that the two sets of duplicate bundles are invisible to each other.
In order to clean up when bundles are uninstalled, this is also a bundle {@link EventHook}.

Thread safe

@author gjoranv
jdisc_core/src/main/java/com/yahoo/jdisc/core/BundleCollisionHook.java