Bundling copy of MIT licenced 'six' v1.4.1 by Benjamin Peterson
Use six.move.urllib to reduce 2to3 changes
Don't need the 2to3 urllib fixer anymore.

$ 2to3 --no-diffs -n -w -f urllib BioSQL Tests Doc Scripts
RefactoringTool: No files need to be modified.
Replace 'raw_input' with Python3 style 'input' via Bio._six.moves
Don't need the 2to3 raw_input fixer anymore.

$ 2to3 --no-diffs -n -w -f raw_input Bio BioSQL Tests Doc Scripts
RefactoringTool: No files need to be modified.
Use six.moves instead of future_builtins
Remove hack for Python issue 19111, using six.moves instead.

We've replaced 'from future_builtins import x' with
'from Bio._six.moves import x' instead.
Remove an xrange doctest to avoid 2to3 change
Use six.moves.range so we can drop the 2to3 xrange fixer
We don't need the 2to3 xrange fixer now

$ 2to3 --no-diffs -n -w -f xrange Bio BioSQL Tests Doc Scripts
RefactoringTool: Refactored Bio/Nexus/Nexus.py
RefactoringTool: Refactored Bio/motifs/matrix.py
RefactoringTool: Refactored Tests/test_GenomeDiagram.py
RefactoringTool: Files that were modified:
RefactoringTool: Bio/Nexus/Nexus.py
RefactoringTool: Bio/motifs/matrix.py
RefactoringTool: Tests/test_GenomeDiagram.py

These changes are all false positives.
Use six.moves.builtins in Bio.bgzf

This reduces the 2to3 changes, but does not address
the docstrings in Bio.bgzf yet.
Don't need 2to3 itertools and itertools_imports fixers anymore

$ 2to3 --no-diffs -n -w -f itertools -f itertools_imports Bio BioSQL Tests Doc Scripts
RefactoringTool: No files need to be modified.
Replace basestring with six.strings_type
Disable 2to3 basestring fixer, using six.string_types instead
Mention bundling of Benjamin Peterson's 'six' library in NEWS file
Import cPickle via six.moves
Import Tkinter via six.moves in Bio.SeqUtils
Import StringIO via six (can't use cStringIO here)
Tweak Bio/bgzf.py doctests not to need 2to3
Make these doctests work unchanged on Python 2 and 3