export_dae.py is making the mesh non-manifold

[hkunz]

When you export using Blender's default legacy Collada exporter, the mesh stays manifold but for export_dae.py, the script is unnecessarily separating the sides of the mesh making it non-manifold which causes problems in other engines like BeamNG. Could you kindly point us to the code that does this separation which we can then comment out for personal use?