Fix: box-sizing: border-box would cause column misalignment when scrolling

- It is far from uncommon to do `* { box-sizing: border-box; }` at the
  top of your CSS these days, including in frameworks, but this could
  cause DataTables a little bit of a problem when scrolling both
  horizontally and vertically since the padding it adds to the header
  linear element to allow it to scroll over the vertical scrollbar would
  be folded into the width of the div linear, rather than added to it.

- Fix is to simply set the box-sizing for the linear. I've decided to do
  this in Javascript rather than CSS since it is going to be needed
  regardless of the CSS being used.