SWIG updates

Not sure the `version` parameter is the correct way to do this, but I didn't see another way. Normally, one could just add a different version to the profile, like this:

    packages:
      swig:
        sources:
          - key: tar.gz:v3xpuif34hadxlhsh4fptz6wde7ixad3
            url: http://downloads.sourceforge.net/swig/swig-2.0.8.tar.gz

However, that isn't enough in this case since we also have to set the version number in the `SWIG_LIB` variable in `when_build_depenency`.