Minor fix for unit test (dependency on Wicket)

I am going to extend this excellent framework to support Vaadin 7.1, Server Side Push (Atmosphere + WebSockets), Guice, and Shiro.

I will try to minimize possible changes, and create separate Vaadin modules; although I believe Vaadin and Wicket can coexist in the same application (compare with Portals: those such as Liferay are JSP based, but can run Wicket, Vaadin, and even PHP).

So, "coexisting" Vaadin + Wicket is probably best solution... need to sync VaadinSession, ShiroSession, and etc.