cmake: fix SWIG Python module compilation

By default, cmake takes the "newer" python installation available.
Since it could be python 3.x, we force by default using python 2.x
option ENABLE_PYTHON3 can force the use of python 3.x back

At the moment, we can't compile both version at the same time, needs
some more hacking on the build system.

fix #293
SWIG: add generated code from SWIG 2.0.x