Clarify no forums available message

Often phpBB will give guests a misleading message when on the index page. It will save "This board has no forums" when in fact the board usually does have forums, but none of the forums can be viewed by guests. This suggestion requests this message be qualified such that if there are any defined forums in the database, it says something like "This board has no publicly viewable forums". Of course, if there are in fact no forums defined, the first message could be shown.