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

fixed full-quadrangle recombine algo:

- run globally, not for each surface
- assign entities to elements
- split line meshes
- correctly re-tag vertices as 1st order
- plug memory leaks

replaced ExportLCField with ExportMeshStatistics (lc + gamma, eta, rho + elem num)

removed unused stuff + handle SURF_DISCRETE in MeshDiscreteSurface

add num of physical groups in stat window

Fixed performance problem(s) for very large meshes with a huge number of
physical entities:

1) use a temp tree for physical entities in read_mesh

2) we should not set partition=physical for the old mesh format

3) only do getFirstPhysical in draw_mesh if we need to (and warn if
   we do and if there are many many physicals)

polih previous commit