Per-file 2to3 settings (most files unchanged, much faster)

Now down to two meaningful fixers, nonzero and unicode
(plus the future fixer which can be omitted):

$ 2to3 --no-diffs -n -w -f nonzero Bio BioSQL Doc Tests Scripts
...
RefactoringTool: Files that were modified:
RefactoringTool: Bio/SeqFeature.py
RefactoringTool: Bio/SeqRecord.py
RefactoringTool: Bio/Phylo/BaseTree.py
RefactoringTool: Bio/SearchIO/_model/hit.py
RefactoringTool: Bio/SearchIO/_model/hsp.py
RefactoringTool: Bio/SearchIO/_model/query.py

$ 2to3 --no-diffs -n -w -f nonzero -d Bio BioSQL Doc Tests Scripts
RefactoringTool: No files need to be modified.

$ 2to3 --no-diffs -n -w -f unicode Bio BioSQL Doc Tests Scripts
...
RefactoringTool: Files that were modified:
RefactoringTool: Bio/Entrez/Parser.py
RefactoringTool: Bio/Phylo/BaseTree.py
RefactoringTool: Bio/Phylo/PhyloXMLIO.py
RefactoringTool: Bio/SearchIO/BlastIO/blast_xml.py
RefactoringTool: Bio/_py3k/__init__.py
RefactoringTool: BioSQL/BioSeq.py
RefactoringTool: Tests/test_Entrez.py
RefactoringTool: Tests/test_PhyloXML.py
RefactoringTool: Tests/test_SearchIO_blast_xml.py
RefactoringTool: Tests/test_SeqIO_SeqXML.py

$ 2to3 --no-diffs -n -w -f unicode -d Bio BioSQL Doc Tests Scripts
RefactoringTool: No files need to be modified.