more fixes for netgen

Added hooks to optimize our meshes using netgen (in particular: the "special"
volume 99999 is now cleaned up after use and all the elements/vertices are
transfered back into the original volumes)

As a bonus, this finally allowed me to remove the ugly hacks in the volume
mesh drawing routines...

optimize netgen mesh import (much much faster now for large meshes)

- revert the OPTIM change on 3D_Mesh.o
- fix bustage for --disable-netgen

keep netgen in make source

refactor the netgen code in a dedicated class

Merged Netgen 4.3.1: a Delaunay/Frontal 2D/3D mesh generator.

Thanks a lot to Nicolas Tardieu for this!

Merged Netgen 4.3.1: a Delaunay/Frontal 2D/3D mesh generator.

Thanks a lot to Nicolas Tardieu for this!

Store the surface orientations (from surface loops) in the volume: we need
this for Netgen.

mention explicitly if a plugin only works for simplices

Generalized Plugin(Triangulate) to handle vector and tensor views

Removed the orientation hacks completely. Should be pretty clean now.

set default RecombineAngle = 75

- %.1g -> %g to display bounding boxes
- update credits

Replaced my orientation hack with a rigorous algorithm... Seems to
work nicely (and is general).

Apply the surface re-orientation hack to quadrangles (and to extruded
meshes!)

isolate the hack in a subroutine

another quick hack for non-convex surfaces

pretty print shortcut help

Yesterday's fix wasn't quite right. This should be better.

Horrible hack to fix the surface orientation problems. This is only a
temporary solution: I don't have time to investigate the issue further
right now...

- mesh.algo -> algo2d and algo3d
- replaced most of the remaining radio buttons with Fl_Choices (requires
  less screen real estate)

create the default project file in the home directory if no "current"
directory is defined (e.g. when double-clicking on the icon on Windows/MacOS)

reset the input lists (do not delete them)

Do a default List_Create in List_CreateFromFile instead of returning NULL.
(This fixes the problems in Plugins that assume that the element lists
are all ready to be added into.)

forgot to destroy the evaluators

nbU -> nPointsU

replace CutCircle/CutCurve with CutParametric

explain that fltk needs to be configured with --enable-cygwin on windows

forgot to deal with quadrangles here