Buffered disk IO stream mess

This is *not* merge-ready. :exclamation: 

This is my second attempt at tacking on some IO buffering from RPython.  I'm prepared to keep attempting, or let someone else do it right.  Tests and specs pass, but translation is failing for seemingly unrelated reasons, but it *must* be related since translation on master is fine.  Hopefully it fails the same way on Travis.

Want feedback please :smiley_cat: