std.rational -- update and progress towards review

[Joseph Rushton Wakeling]

On 05/10/13 00:40, Brad Roberts wrote:
> That's not an argument against splitting the changes up and getting the
> dependencies handled first.  It's an argument to do a good job with both sets of
> changes, which I agree with.

I've submitted a first supporting pull request:
https://github.com/D-Programming-Language/phobos/pull/1616