small opti

For all our mechanical engineering friends out there, I just cleaned up the stuff
I did with Sean last year, i.e., allow to draw a vector field as a displacement
map, with another scalar field displayed instead of the displacement norm.

It's basically the same as Plugin(DisplacementRaise), but it does not modify the
actual data inside the view (so e.g. you cannot save it). Instead, it's implemented
as an alternative "Vector display" mode. This allows to easily animate deformed meshed
with arbitrary scalar fields drawn on them. (The GUI for this is kinda lame, but
it works: just select Vector display->Raised scalar view, select the scalar view
number, et voila.)

I also generalized the smooth normal code path a little, so that we can have smooth
normals for vector-as-displacement and tensor-as-von-mises plots, too.

fix spelling

- set glBlendEquation explicitly
- make parser

old comment

moved the footnotes at the end of the page

1.55

minor text mods

add missing #ifdef HAVE_FLTK

revert changes

make code compile on Mac again

better label for "constrain bg mesh"

fix support for multiple light sources (+ add a couple of options to set
the light color and specular reflection exponent)

typo

Don't call Mesh_Quality() in GetStatistics()

added vertex arrays in volumes to store the boundary of the cuts
when we draw them "as surfaces" (for Philou, not tested yet)

fixed small bug in ReplaceDuplicateCurves where we woudn't eliminate
identical CIRC/CIRC_INV ELLI/ELLI_INV pairs

re-add return statements in functions returning non-void. JF: my compiler
wants this (and he's right)

small copy/paste mistake in my last commit

make depend

- fixed a couple of gcc warnings + added missing o->end() in
  jf's StructuralSolver plugin

- fixed the view option code: FLTK > 1.1.5rc1 breaks our use of
  widget->changed()...

- added background mesh support in the aniso algorithm

- fixed a couple of corner cases in the computation of 2D/3D isos
  (+renamed the routines)
- fixed small box size bug in the GUI

airplane work: reorganized the option panels in the GUI (more descriptive
labels, same categories for geo/mesh/post, etc.)

draw the clipping/cut plane dynamically when we change the coefficients

added an option to cut only volume elements

draw intersection of cutting planes with the bounding box

- added an option to draw the bounding boxes

- simplified the color_scheme options

- added tooltips to make the discovery of shortcuts easier

- added Orientation() members for hexas, prisms and pyramids

- use det3x3() instead of ad-hoc code everywhere it makes sense

little hack to visualize overlapping multi-patch spheres with constant
offsets (use timeStep<0...)

add "post-processor" keyword

add "reset" button in clipping window

clip plane doc update