cleaner cut plane tests

- added little GUI for mesh cutting plane
- added option to draw the intersecting layer as surfaces

modify alt+shift+l to match the old behaviour

document second order simplices

- order 2 doc is done
- order 2 drawing is fone

added drawing code for faces of haxahedra, prisms and pyramids

removed the Mesh.Solid option: it's not necessary anymore

added drawing code for faces of 2nd order tets

Damn, "Palette" is defined in the Carbon API. Change it to "PaletteContinuous".

- allow to draw geometry tangents/normals even if the actual
lines/surfaces are not

- cleaned up draw_nonplane_surface

fixed (?) log scale for continuous maps (and maps where we don't check
for IntervalsType: scalar points, etc.)

restructured our rather liberal use of POLYGON_OFFSET_FILL (much better
now: it doesn't interfere with the glut primitives anymore)

simplified Draw_Simplex_Surface

use slightly larger arrows by default (60 pixels instead of 50)

more small cosmetic tweaks:

- don't display the big axes by default anymore (they're not as useful
  as they used to be, since we compute the rotations around the
  pseudo cog instead of the origin)
- set the default opengl font size to 12 (instead of 11)
- add some space between the scales and the labels (10 pixels instead
  of 5)

increase geom line width even more (2 pixels)

Refined mesh drawing code:

- draw surface element edges and/or faces
- draw volume element edges and/or faces
- consistent color choices between surface and volume elements
- wider geometry lines
- better defaults

better positioning of text labels on mesh and geometry

better test to check when to abort parsing

- define edges_XXX only once

- draw slightly larger/visible mesh points

- make t1.geo/t2.geo faster

- Added nice little buttons in the mesh menu to choose between 1st and
2nd order interactively

- Added 2nd order mesh stats in the GUI

- converted 2D_Recombine and SecondOrder to the EdgesContainer class
- removed the quadrangle hak and the ugly EdgesInVolume global from 3D_Coherence

nicer layout of mesh color pane

copy & paste buglet

- Fixed second order mesh generation in 3D (on simplices only at the moment).

- In prevision of the extension to hexas, prisms and pyramids, all elements
are now derived from a new Element base class, which will be used in the
generalization of Edge/EdgesContainer in the future.

Improved xytouv() and xyztouv() by trying different initial guesses in the
newton algo (before relaxing). Should be more robust than what we did before.

added new constructor with no arguments in prevision of Degre2 cleanup

Fixed computation of vertex->u param in curve extrusion

- Fixed drawing of 2nd order triangles and tets
- Restored drawing of 2nd odrer vertices in different color

cleanuip (removed duplicate code) + new function u() to get the abscissa
more easily

better progname