I'm not sure that converting to bytes for Python 3.0 is going to
be a simple change.  For one thing, most of the arithmetic functions
have to do the reverse conversion (int -> str/bytes) at some point.

At the moment, an int -> bytes conversion has to go through unicode (I 
think);  something like  bytes(str(n), 'ascii'), so it's not 100% clear
that replacing str with bytes is going to produce a speed gain.

For now, I'll get the fix for the 2.5/2.6 problem in (it only
involves changing 3 lines in decimal.py, along with adding a few
extra tests).

Changing str -> bytes in 3.0 needs more careful thought, and some 
benchmarking.