Make pytools get by without 2to3

pytools/__init__.py

pytools/arithmetic_container.py

pytools/batchjob.py

pytools/convergence.py

pytools/datatable.py

pytools/debug.py

pytools/decorator.py

pytools/diskdict.py

pytools/lex.py

pytools/log.py

pytools/mpi.py

pytools/mpiwrap.py

pytools/obj_array.py

pytools/persistent_dict.py

pytools/prefork.py

pytools/spatial_btree.py

pytools/stopwatch.py

pytools/test.py

setup.py

test/test_data_table.py