add dispatch for python2 and python3

hi.
when I use curdling in python3.4, `AttributeError: 'module' object has no attribute '_levelNames'` occured.

So, I tryed to add dispatch for python2.x and python3.x.
(I tested python2.7 and python3.3, python3.4)

At last, sorry for my too poor English and python ;-(