update RMI tutorial to reflect useCodebaseOnly default change to true

In JDK 7u21 or thereabouts, the default value of the useCodebaseOnly property was changed to true. The examples in the tutorials should be updated to reflect that. Either they should be changed to set useCodebaseOnly to false (probably not a good idea) or they should be changed to set the codebase property to the URL of where the dynamically-loaded code resides.