class Prawn::Table

def add_header(row_number, cells_this_page)
  x_offset = @pdf.bounds.left_side - @pdf.bounds.absolute_left
  header_height = 0
  if row_number > 0 && @header
    y_coord = @pdf.cursor
    number_of_header_rows.times do |h|
      additional_header_height = add_one_header_row(cells_this_page, x_offset, y_coord-header_height, row_number-1, h)
      header_height += additional_header_height
    end        
  end
  header_height
end