anchor.diff:                      // another page.
                       if thisPageNumber = boundaryPageNumber then
                           pb.SetPageFlag FLAG_BOUNDARY_NODE
  -                        let newRange = pageManager.GetRange(token)
  -                        nextPageNumber <- fst newRange
  -                        boundaryPageNumber <- snd newRange
  +                        let (nextPage,boundaryPage) = pageManager.GetRange(token)
                           // assert pb.Position <= (pb.PageSize - 4)
  -                        pb.SetLastInt32(nextPageNumber)
  +                        pb.SetLastInt32(nextPage)
  +                        nextPageNumber <- nextPage
  +                        boundaryPageNumber <- boundaryPage
                       else
                           nextPageNumber <- nextPageNumber + 1
                       pb.PutInt16At (OFFSET_COUNT_PAIRS, countPairs)
  
positive.code:                 pb.PutInt32(valueOverflowFirstPage)
              lastKey <- k
              countPairs <- countPairs + 1
          if pb.Position > 0 then
              // note similar flush code above
              let thisPageNumber = nextPageNumber
  
negative.code:             pb.Flush(fs)
              if nextPageNumber <> (thisPageNumber+1) then utils.SeekPage(fs, pb.PageSize, nextPageNumber)
              nodelist.Add(thisPageNumber, lastKey)
  
          // all the leaves are written.
          // now write the parent pages.
          // maybe more than one level of them.
          // keep writing until we have written a level which has only one node,
          // which is the root node.
          if nodelist.Count > 0 then
              let firstLeaf = fst nodelist.[0]
              let lastLeaf = fst nodelist.[nodelist.Count-1]
              while nodelist.Count > 1 do
                  let (newNextPageNumber,newBoundaryPageNumber,newNodelist) = writeParentNodes pageManager token firstLeaf lastLeaf nodelist nextPageNumber boundaryPageNumber fs pb pbOverflow
                  nextPageNumber <- newNextPageNumber
  