better z-clipping planes for perspective proj (should also work for objects
far off the z=0 plane now)

make depend

InitRenderModel should be called before InitPosition (to have fixed
light positions)

added small slider window to choose the z-clipping factor in real time.

FLTK is really awesome :-)

better perspective projection handling (around cog+new icon in gui)

fix lasso zoom drawing

refactored Opengl_Window.handle()

should behave exactly like the old version, but now it is at least (somewhat)
readable and ready to be generalized for more complicated projection matrices

add line elements in octree + little nicer Probe drawing

avoid repeated error msgs

print option dialogs now also show up when saving files "by extension"

cleanup+add comments so that students can understand what's going on with
the projection stuff.

(still need to cleanup the zooming in handle() to use gluUnproject() instead
of the ad-hock stuff that only works for an orthographic proj)

little hack to draw a gradient in the background. Nice for flashy
presentations ;-)

better label for "save all"

bug fix when using "rough algo" to create the mean plane: the normal
was computed with reserve orientation compared to the normal case.

better accuracy for normals

- Ctrl+w should close windows on non-Mac and non-Windows archs
- Escape should close dialogs on all archs

nicer GUI for special viewpoints:

* added "90 degrees rotation around axis perpendicular to the screen" button
  (+90, or -90 when holding Shift)
* clicking on X,Y,Z buttons with Shift now gets the view "from behind"

little hack for philou: clicking on "Z" while holding "Shift" will cycle
through 90 degrees increments of rotations around the Z-axis

add links to new interactive tutorials

some new examples

link to new gui tutorial about visualizing deformations

getFirstPhysical -> getLastPhysical, so that the coloring gets made according
to the latest physical entity created instead of the first one.

Requested by philou; most interesting when creating physical groups on
existing meshes.

say explictly that LaTeX XXX part output is without text

reverting last change: it's nicer to always have the z axis pointing up