Enhancements for Py3K support

I am working on getting supervisord to run on Python 3. I started with meld3 and made the minimum changes required to allow it to run on both Py2 and Py3. The oldest version of Python I have on my Mac is 2.5, but I believe that all changes should at least run on 2.4. It may work on 2.3 but I don't know enough about the differences between 2.3 and 2.4 to say for sure. I made simple inline changes rather than using six.

Interestingly, getting meld3 to run on Py3 exposed a segfault in the latest Python 3.3.0 when processing XML. I have verified this with the pre-built version on my Mac and a source-built version on Linux.

Anyway, I hope you will consider accepting my changes. It was a bit more work than I had expected due to changes in the XML library.

Best,

Scott Maxwell