The rewrite of the geometry and mesh drawing code is complete.

There is still room for optimizations, but mostly at the level of the
algorithms (edge/face generation, striping, etc.)---changes that will
be easy do do thanks to the new much cleaner interfaces.

From preliminary tests (even without new algorithms) the code seems to
be faster (a LOT faster for volume meshes) and to use quite a bit less
memory.

I'm tagging the trunk as "gmsh_2_0_alpha_1".