Complex and Rational are now built-in to 1.9

Just when I thought I'd finished documenting the standard library for the new PickAxe, I did one last svn up of the Ruby interpreter source and discovered that the Complex and Rational classes are now builtins—no need to require the library to get the basic functionality. The change also affects a number of other built-in classes (you can now say nil.to_c, for example). I'm not 100% sure I agree with rolling in Complex, but the addition of rational numbers is a welcome change.

Unfortunately it's back to the drawing board on my plans to release a new beta today...