Improve clone.py script to be compatible also for python 3.2.X

see http://answers.nuxeo.com/questions/1073/using-python-32x-on-windows-to-clone-git-repository

Traceback (most recent call last): File "clone.py", line 144, in <module> assert_git_config() File "clone.py", line 137, in assert_git_config if "always" in t: TypeError: Type str doesn't support the buffer API

whereas it works fine with Python 2.7.x.