Merge improve-rbigint. This branch improves the performance on most long operations and use 64bit storage and __int128 for wide digits on systems where it is available.
Special cases for power of two mod, division, multiplication. Improvements to pow (see pypy/translator/goal/targetbigintbenchmark.py for some runs on my system), mark operations as elidable and various other tweaks.
Overall, it makes things run faster than CPython if the script doesn't heavily rely on division.