findChangedPages :: Repository -> RevNum -> RevNum -> IO (Set PageName)
findChangedPages repos 0 newRev = findAllPages repos newRev
findChangedPages repos oldRev newRev
findChangedPages :: Repository -> RevNum -> RevNum -> IO (Set PageName)
findChangedPages repos 0 newRev = findAllPages repos newRev
findChangedPages repos oldRev newRev