code: public static CallbackHandler deactivateCallbackHandler(GSSCredential cred) {
  	if (cred == null) {
  	    return null;
  	}
  	CallbackHandler handler =
  	    (CallbackHandler)callbackHandlers.remove(cred);
  	if (handler == null) {
  	    return null;
  	}
  	handler.shutdown();
  	return handler;
      }
docs: Deactivates a callback handler for a given credential.
  
  @param cred the credential of the callback handler.
  @return the callback handler that was deactivated. Null,
  if no callback handler is associated with the credential