[OE-core] [PATCH 28/45] swig: move to Python 3

[alexander.kanavin at linux.intel.com]

>
> It would be nice to use PACKAGECONFIG to select 2 versus 3 so we can
> build sdks that only have python2.

This requires a conditional class inherit (pythonnative vs.
python3native), which you can't at the moment do with PACKAGECONFIG.

If you really need this, make a swig-python2 recipe.

Alex