Remove pointless import
Switch a StringIO import to use Bio._py3k
Use Bio._py3k.getoutput in dnal code
Remove unused 'import commands'

This is something 2to3 replaces with 'import subprocess'.
Make this example StringIO import work under Python 2 and 3
Minor style improvement to _py3k type checking
Mention less 2to3 fixers used for faster r install on Python 3