missing line_width/point_size calls

- plugin callbacks now draw their stuff until run/cancel is executed (so we
  manipulate the scene with the additional data displayed)
- made plugin code much shorter
- simpler defaults for StreamLines, CutGrid and Evaluate

- new alternative Draw_String function taking a "style" argument (used
  only for font size at the moment)
- new Plugin(Annotate) to add simple text strings to a view

add color options for elements in views (requested by Philippe a long
time ago)

double precision of middle cross drawing

nicer stippling patterns

update to latest gl2ps

fix non-proportional arrow display at the COG

- Moved all the Raise[][] stuff out of the drawing routines, and into
  Graphics/Post.cpp

- New 'generalized raise' mode (can use arbitrary expressions, possibly
  with external data sources, to raise/offset views dynamically). Original
  patch by Nicolas Tardieu. Merci Nico!

- moved the AdaptiveView stuff in its own header file

- fixed small bug in IsoSimplex (when Raise != 0)

- fixed small memory leak in Plugin/Extract (when one or more
  expressions are invalid)

This patch fixes an old design flaw in the post-processing module,
namely that we used a list of Post_View objects instead of a list of
pointers to Post_View objects in CTX.post.list.

This had many annoying consequences, in particular the fact that we
needed to be extra careful every time the list was reallocated (as
pointers to the list elements would become invalid).

I tried very hard to change the code everywhere it should be changed,
but I might have missed something. Please let me know if you see
anything suspicious (like a crash when you duplicate/remove/combine/...
post-processing views).

better solution for offset

fine-tune epsilon

better epsilon

update to latest gl2ps

The "Simplex" class is now derived from a new class "SimplexBase",
which contains only pointers to the nodes, and none of the other stuff
necessary for the actual mesh generation.

All the input/output/display routines have been rewritten in terms of
SimplexBase: this provides a gain of almost 50% in memory when you
just load meshes from .msh files to do visualization stuff, instead of
actually generating the mesh.

New General.ClipFactor option to fine-tune the position of the near and far
clipping planes (default = 10; setting a smaller value leads to a better
z-buffer resolution, but zooms/rotations can then lead to undesired clipping).

Revert to GL_NORMALIZE instead of GL_RESCALE_NORMAL (since GL_RESCALE_NORMAL
is not supposed to work with anisotropic scalings)

- First draft (pretty much untested!) of new "Integrate" plugin to
  * integrate scalar fields over all the elements in a view
  * integrate the circulation of vector fields along line elements
  * integrate the flux of vector fields across surface elements

  Used with Plugin(DisplacementRaise) and Plugin(Evaluate) this
  permits for example to compute the area/volume of deformed
  configurations; and, with Plugin(CutPlane)+Plugin(Skin), the
  perimeter of deformed sections. Another interesting application is
  to use it on a vector field with Plugin(CutPlane), in order to
  compute fluxes across arbitrary cross-sections.

- Added "connectPoints" option to Plugin(CutParametric) so
  that we can feed its output to Plugin(Integrate)

- Added Normals and Tangents options to visualize the orientation of
  elements in post-processing views

- Added "swapOrientation" in Plugin(Transform) to change the
  orientation of the elements (in place) (+ moved the transformation
  routines from the view class into the plugin)

- fixed #defines in some of the plugin header files

better error messages+choice selection for "external view" stuff

trying to fix problem reported by T. Schumacher: use double[16] instead of
double[4][4] for opengl matrices

New (very simple, but very nice IMHO) callback mechanism in plugins: a
plugin can now set the min/max/step in input fields, and draw
arbitrary stuff when the values are modified.

This makes the plugin interface MUCH nicer: the plane in CutPlane is
defined interactively (a la "Clipping planes"), the sphere in
CutSphere is visible, the min/max values in CutMap reflect the min/max
in the view, etc.

proof of concept for unproject (e.g. to add points with the mouse)

- make the rotation matrix a matrix of doubles (instead of floats)

- store the modelview and the projection matrices in CTX

- new unproject() routine to transform window coordinates to model
  coordinates

- cleaned up all the static variables in the Opengl_Window class

- small fix to reduce normal clamping when zooming

small cleanup + better error detection

The new "External data source" option makes the "Vector type->Raised
view" unnecessary. Just select "Vector type->Displacement" and choose
the data source from any other view in the list--including "Self"!

added small option to color the arrows representing a vector field
according to the data from another view

new option to draw the arrows with a fixed size

shorter Draw_TensorElement routine

make displacement drawing code much shorter

Generalized "Raised scalar view" vector type: one can now also raise
vector and tensor views. (It's now simply called "Raised view".)

draw the labels a little bit closer to the entities

added ability to save views in "parsed" format

added an option to draw the nodes per element (much slower, but permits to
visualize only a subset of the nodes)

one last touch :-)

more fine-tuning

fine-tune size

fixed alignment problem when views have different View.Formats