debian fix, take 2: only apply for uname=Linux

trying to fix Debian bug (fltk-config does not return opengl libs anymore)

OCCFace::containsPoint() did not correctly take orientation of edge loop
into account (fixes bug reported by Jacques Kools about cross in OCC plane
faces not drawn)

commited. It allows to remove self intersecting meshes in
the 2d mesh generation process. It only applies now to
gmsh native CADs. Those limitations will quicky go away

make clear in docs that node/elemement tags should be > 0 (and not == 0)

- fixed remeshing of boundary layers when geo entities are constructed
using bnd layer points (no need to reload the file from scratch anymore
to avoid accumulating the transformations)

- patch load_gmsh.m for .msh version 2 (patch from Raoul)

- new load_gmsh2.m from the mailing list

added option to draw skin of 3D meshes

tweak color + add comment with default values from Solid Works and Catia (if
we want to imitate :-)

- made "light" color scheme the default
- lighter colors for "light" scheme

removed global THEM

(once more step towards nicer integration of old GEO stuff)

add option to test auto skin stuff

add option to test automatic skin stuff

add experimental support for automatic on-the-fly boundary computation
in vertex arrays

- don't force show geom surf/vol if we have a mesh
- removed unused stuff in VertexArray before moving to set<ElementData> for
  auto boundary creation

only make tri unique in 3d

manage GModel::list automatically (like PView::list)

fix BDF small field export on Windows (apparently Windows does not conform
to ANSI C and uses 3 digits in %e instead of 2)

remove dependency on FLTK 1.1.7 (replace call to Fl::screen_xywh with call to Fl::w)

compatibility fix: make arrows scale like in the old version

better normals