better test for invalid For/EndFor loops

more robust "Delete Empty Views"

my last commit also fixed several problems in For/EndFor loops:

- the body of the loop was executed at least once, even if the test was
  always false (e.g. For (1:-1:1) )
- the body could be executed one extra time when using optional
  step values
- the for loops didn't work with negative step values

- new parser function GetValue("text", default_value) to query a value
  interactively in a script

- added a nice example using this (to compute slices automatically):
  demos/multislice.script

- new "Delete Empty Views" command
- new View.MinX, View.MinY, View.MinZ, View.MaxX, View.MaxY, View.MaxZ options
- added example on how to do simple volume visualization

- fix cast in a couple of error msg
- more fixes in elliptic algorithm (surf->TrsfVertices and surf->Vertices
  were incomplete)

one can now specify a TIME list of values in parsed views to give the
values of the time (or whatever) steps (like in ascii/binary views)

- Added a bunch of colormaps from:

  Color Theory and Modeling for
  Computer Graphics, Visualization,
  and Multimedia Applications

  Haim Levkowitz
  University of Massachusetts Lowell
  Lowell, Massachusetts, USA

- Increased max size of colormap to 1024

- Small cleanup in parser+plugin

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).

fixed error checking code to work also with adaptive views.

cleanup (and remove 2 shift/reduce conflicts in parser)

New high order interpolation.

JFR

forgot to commit this

generalized the "spatial" Combine so that we can also combine by view name

cleaned up View->Combine by defining a new option (to determine if
we should remove the original views after a "Combine" or not)

speedup view removal (only call UpdateViewsInGUI once per group of
deletions)

- set glBlendEquation explicitly
- make parser

force a buffer flush when we abort the parser due to too many errors

- All extrusion commands now return a list of 2 numbers (instead of 1):
  the first, as before, is the number of the "top" of the extruded region
  (i.e., a point for extrude point, a line for extrude line, ...), the
  second is the number of the "body" of the extruded region (i.e., a
  line for extrude point, a surface for extrude line, ...).

- "Extrude Surface" now always creates a new volume (automatically),
  EVEN WHEN THERE IS NO LAYERS SPECIFICATION. This makes it consistent
  with "Extrude Point" and "Extrude Line", which always create new
  curves and surfaces, respectively.

  Important Note: you will have to modify your old .geo files to avoid
  duplicate volume definitions if you use "Extrude Surface" without
  extruding the mesh (i.e., without the "Layers" command). These
  duplicate volumes would be harmless, but they would srew up your
  physical volume definitions later on...

  * Solution 1: use the new volumes (recommended). To do this, just
  remove your old extra volume definitions and let Gmsh create the
  extruded volumes for you. (To retrieve the volume number created by
  Gmsh, use "aa[] = Extrude Surface {...};;": the volume number is
  "aa[1]".)

  * Solution 2: keep the old volumes.

  a) clean way: retrieve the new volume number (aa[] = Extrude Surface
  {...};;) and delete the new volume with "Delete { Volume aa[1]; }"

  b) dirty (but handy) way: since, in order to create the new volumes
  with the less impact possible, Gmsh uses "low" numbers (actually,
  forcing "Geometry.OldNewreg=0") for the new volumes, just remove all
  "low number volumes". For example, if you have 4 "Extrude Surface" in
  your file, you can then just do "Delete{ Volume {1:4}; }"

Voila :-)

bulletproof FindCurve/Surface + uniformize error messages

add @. after color specs in Fl_Browser: otherwise strings that start
with a digit don't get printed

- set VectorType to Displacement in Plugin(StreamLines)
- shout when a plugin option/name does not exist

new BoundingBox command to force the computation of the bounding box (useful
when there is no geometry and we don't include/merge any views)

- generalized vertex arrays to handle quads

- added missing Ellispe ... Plane ... in parser

Added final bit for 2nd order elements: the middle face nodes for
quadrangular faces (i.e., for quadrangles, hexahedra, prisms and
pyramids).

- removed the quads from the simplex trees (finally...)

  **warning**

  this is a pretty big patch that touches a lot of different files. I
  tried my best to update all the things that needed to be updated,
  but I probably forgot some things... Please test! (especially the
  export routines in obscure formats like SMS, Gref, etc., as well as
  the extrusion code)

- added second order edge vertices for hexas, prisms and pyramids
  (drawing not done yet)

- added sanity check for number of values in post-pro parsed file
  format

- merged all mesh printing/reading routines in Print_Mesh.cpp and
  Read_Mesh.cpp

- cleaned up the statistics code

make parser

issue a small warning if we try to include or merge an unexisting file
in the parser

- store the points required by the transfinite algo in a list of vertices
  (instead of surf->ipar, vol->ipar)

- generalized Coherence for these lists of transfinite points

- added hacked version of the GNU matheval library to evaluate parsed
  functions efficiently ("a la getdp", but faster): I added a new
  directory (gmsh/MathEval) with that code, as well as a new configure
  option and a new define (HAVE_MATH_EVAL)

- generalized the plugin option code to accept arbitrary string options

- new plugin Plugin(Evaluate) that can evaluate arbitrary functions on
  scalar views (useful for example to create background meshes)

PS: Everything (octree + function evaluation) is now in place to write
a general plugin that can make any operation between arbitrary
views...

better test to check when to abort parsing

make parser && make depend

- Simplified the bounding box computation. It is now computed as
follows (after each include/merge/open):

1. If there is a geometry (i.e., at least one geometrical point), the
bounding box is taken as the box enclosing all the geometrical points;

2. If there is no geometry but there is a mesh (i.e., at least one
mesh vertex), the bounding box is taken as the box enclosing all the
mesh vertices;

3. If there is no geometry and no mesh, but there are some
post-processing views, the bounding box is taken as the box enclosing
all the primitives of the last post-processing view.

This should fix the weird things that sometimes happen when we animate
scenes that do not contain any geometrical entities.

- Deprecated MergeWithBoundingBox()

- Removed Replot()

- Removed the "Last_NumberOfPoints" hack in the parser

- Removed CTX.expose

Fixed '//' with EOF before '\n' bug

And more airplane work!

- merged STL patch from Nicolas Tardieu. This patch permits to
  create an real elementary surface for each STL face. Until
  we have some code to directly remesh the STL data (which would
  be much nicer and cheaper), this is very useful. We can finally
  use STL representations to create meshable volume models.
  Thanks Nicolas !

- new option to color the mesh by physical entities (if an element
  belongs to multiple physicals, we use the first one)

- additional cleanup of the mesh drawing code

- big cleanup of the geometry creation section in the parser:

  * removed horrible Geo/DataBase.cpp
  * fixed all List-related memory leaks (a lot!)
  * added tests to check if we don't try to recreate existing
    entities (this should prevent many weird bugs due to incorrect
    input files)

- fixed LineLoop/EdgeLoop memory leaks

- many small fixes all over the place

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