Horribly unreliable Arbint's and Rational<Arbint>'s

Changes from before: Arbint's use a division algorithm based on bitshifting.

So, you might get a random segfault (if you scroll you will definitely get a random segfault)
and pretty much every single operation with Rational<Arbints> gives you an accuracy warning...

And yet somehow I can render a Bezier. Really slowly.