Python 3 support

Created by: anjos

Python 3 is already on version 3.4 (an alpha was just released). It is available on MacPorts. It is already the default python in ArchLinux. It will be the default one in Ubuntu as of 14.04 (that is April/2014).

We should slowly try to get the code compatible and ported. Unfortunately, Python 3 is not fully backward compatible with Python 2. So, let's keep in this bug report overall guidelines for porting the code. The idea is that, as much as possible, we try to keep the code in such a way that it is valid in both Python 2 and Python 3. In cases where that would not be possible, we may have to temporarily (until there is only Python 3) introduce if switches.

This work will start with Bob, but should soon propagate to the satellite packages. All help is welcome.

Here is a quick guide of changes to get you started.

I'll create an externals environment and post instructions for compiling against Python 3 at Idiap soon.