[Gmsh] how do we do to export a mesh in med 3.3 from Gmsh 4.2.3

[G. D. McBain]

> So it seems like you cannot create a MED3 file when using the MED4 library.
>
> Maybe you could escalade this to the MED developers?

There was some discussion of this over at

   https://github.com/nschloe/meshio/issues/347#issuecomment-474367765

and it had been raised before that at

   https://www.salome-platform.org/forum/forum_10/835834708

The makeshift proposed in the meshio thread was:

    …MED file, where the version is changed from 4.0.0 to 3.0.0, by modifying manually INFOS_GENERALES.  …This file can be loaded by gmsh