Drop python 3.2 support and move to python 3.3

This PR drops python 3.2 support and move to py3.3 (following Jinja 2.7 release with is only compatible with py3.3, see [this post](http://lucumr.pocoo.org/2013/5/21/porting-to-python-3-redux/)). 
Pelican already supports py3.3, but the functional tests were failing because the feed attributes were not written in a consistent order with different python versions (ref #688 and #729). This was fixed by @avaris (dmdm/feedgenerator-py3k#1, and dmdm/feedgenerator-py3k#3 to fix py2.7 support). With these changes on feedgenerator, the functional tests give the same output with py2.7 and py3.3. However this currently depends on feedgenerator's dev version, waiting for a new release.