Python 2 and 3 simultaneous support (1st step)

[José Matos]

Hi,
        the first step to start the procedure is to update the requirements for 
python to 2.7 as discussed last year.

        My problem is that as described last year I suggest to support python 
== 2.7.x (for any x) and python >= 3.3.0.

        I am at loss how to add this test to configure.ac and similarly to 
cmake.

Any help from our resident experts Jean-Marc and Kornel.
-- 
José Abílio