sixtracklib/common: move object type identifiers to an enum to ensure static const-ness for C99 compliance
sixtracklib/common: move object type identifiers to an enum to ensure static const-ness for C99 compliance

SixTrack/SixTrackLib,SixTrack/SixTrackLib,SixTrack/SixTrackLib,SixTrack/SixTrackLib