[Tachyon-list] Bignum & Unsigned Right Shift

The bignum refactoring for the front-end is pretty much complete and so far all unit tests pass. However, I think there is one feature missing from the bignum code. I would like to be able to do unsigned right shifts in addition to signed shifts.

If you have time, Marc, could you add an unsigned flag to the shift function, and perhaps have it assume signed shift by default? If you do, please make sure to pull the latest code from the repo.

Tomorrow I'll try the boostrap again and see how far we can get. Hopefully I won't have introduced too many bugs in the code I just modified! (fingers crossed).

- Maxime