Add Layer on Extrude Point (phase 2 -- remove duplicates)

Fix crash due to identical vertex pointers in Mesh.Points and
Mesh.Vertices

Indented all source files using utils/gmshindent

Updated copyright

Introduce OpenGL display lists for drawing meshes. Does not seem to
work much faster on my machine, though.

New global volumic extrusion algorithm. New extrusion should now be the same (right or wrong!) as old extrusion...

NOT work: it creates duplicate points, etc.). Sorry!

better handling of opened files (msh+pos)
min/max computation for msh pos