Support large integer operations with RPython's rbigint library

[timfel]

This is not an ideal refactoring, but I hope it helps with performance until full word-sized large integers show up

[krono]

looks ok so far

[timfel]

@fniephaus No, but our argument processing stuff (with "--" and such) just makes it a little more complex to put the "--batch" in the right place. Also, it's annoying when you're developing, because then you might want to stop interactively. Anyway, I moved --batch options to the build-linux script