add missing copyright headers

always save the surface elements in unv format (not just when the surface is
not part of the boundary of a volume)

make depend

moving all external code to contrib subdirectory

use it now with -partition N for N partitions
only works with tets and triangles
output should be added (useless for now)

with node ordering corresponding to positive orientation (volume).
Test implemented for 1st and 2nd order elements, but only 1st order hexas
have actually been tested!

simpler tetgen integration by Jozef Vesely

fix memory leak + missing depend

move msg

compile tetgen by default so we get feedback on machine-specific problems

try different ordering when swapping fails

All modifications are commentarized because
this feature is not functionnal : the transfer from
Gmsh to Tetgen is OK, but the transfer from Tetgen to
Gmsh is not : all the mesh (points, lines,
surfaces, volumes) must be recreated in Gmsh...

New fonction to use Tetgen 's algorithm
Attention : several problems
  - the method deinitialized of Tetgen is not seen by the compiler
  - it seems that the data structure tetgenio is destroyed after its creation,
so that all meshing procedure is dine in the constructor

don't store lines in vol->Simp_Surf : it screws up the saving of Physical
Lines! Use vol->Lin_Surf

remove the VerticesTemp hack, as it was not the main bottleneck

Removed the last bits of the "Discrete Surface/Line" stuff.

Gmsh can now simply read a .msh file, and use it as the boundary mesh
of a 3D mesh. For an example on how to do this, cf.
demos/sphere-discrete.geo.

This complements nicely the STL remeshing stuff: Gmsh can now
for example very easily be used to extrude surface meshes that
come from other tools.

fix old extrude of existing meshes

make full-quad algo work for non-plane surfaces