I re-pickled the data files using python 3 by using code like the following:

    pickle.dump(destpath,pickle.load(srcpath,encoding='latin-1'),protocol=2)

If there's a collections.defaultdict in the pickle dump, python 3.3 pickles it to `UserString.defaultdict` instead of `collections.defaultdict`. I'm however not sure why this is, but python 2.7 and 2.6 do not have a `defaultdict` class in `UserString`, so I've added that as a compatibility fix.