Called when a {@link javax.servlet.ServletContext} is being destroyed.DWR finds out about this destruction if (and only if) in web.xml there is a {@link org.directwebremoting.servlet.DwrListener} registered.This happens before the {@link javax.servlet.http.HttpServlet#destroy()}is called.
If DwrListener is not registered, this will not happen
This method should only be used when we need to take action to enable the servlet to stop cleanly. Typically this will be restricted to stopping reverse ajax threads.