Fix #7 - Right indexing was incorrect when building the reorder points

- _fnRegions creates an array when the drag reorder starts to make the
  mouse move event handler flaster, and it needs to remove the reagions
  which are fixed (left and right), but for the right column, because
  the index saved was in the settings object was the column index,
  rather than the number of columns, the array manipulation was wrong.

- Fix is to store the number of fixed columns rather than the column
  index and work off that.