Generalized Plugin(Extract) so that it can also create tensor views

- generalized the octree code to make it work with all the element
types, and not only with triangles/tets (and fixed a couple of copy &
paste bugs in the process...)

- modified all depending plugins to take advantage of this

- New "Discrete Line" commands (similar to the Discrete Surface commands, but for
  curves).

  This permits e.g. to use Gmsh's extrusion mesh generators on 2D meshes (with
  boundaries) imported from other programs, and have all the useful elements
  generated (both volume and surface).

- Don't use Ctrl+m for File->Merge, as it is a reserved keyword for
  Window->Minimize on OS X:
  * File->Merge is now Shift+Ctrl+o (since it's in some way a variation of
    File->Open's Ctrl+o)
  * Tools->Options is now Shift+Ctrl+n

add "Window" menu on Mac OS X

removed extra white space and node coord format in UNV export

- added new "spectral" colormap (truncated hsv)
- added GUI button for elliptic mesh + geometry coherence
- added GMSH_MAJOR_VERSION, GMSH_MINOR_VERSION and GMSH_PATCH_VERSION
  in the parser

add comments

allow negative line loop number in surface definitions

better Tools->Visibility GUI

small cleanup (+ remove solver link on webpage)

small modification to make the solver interface not block the GUI when the
solver runs without printing messages

- renamed "Duplicate View" into "Alias View" (suggested by Philippe;
  less confusing since "Duplicate" implies that we actually copy the
  data, which is not what we are doing)

- added general "on the fly" tranformation matrix option. This allows
  for very efficient visualization of aliased datasets with
  non-destructive rotations, symmetries, etc.

new plugins: Gradient, Curl and Divergence

- generalized Plugin(CutGrid):
   * now works also for lines/points (i.e., when nPointsU and/or nPointV == 1)
   * new option ConnectPoints

- new Plugin(Eigenvalues)

- don't force color in Draw_PlaneInBoundingBox

- removed all the crappy STL code and rewrote it using JF's POLY_rep
  class

- generalized POLY_rep so that we can use the polygonal discretization
  as a surface mesh, and mesh in 3D afterwards. I.e., we can now take
  an input triangulation (a single surface in STL format, multiple
  surfaces in STL format, one or more surfaces defined using the new
  "Discrete Surface" commands), and generate a 3D mesh that uses it. We
  could in theory even mix triangulated and "normal" surfaces in the
  same geometry, but nothing is done at the moment to ensure that the
  mesh at the interfaces would match (if it does, it actually works
  very nicely)

- new STL mesh output format to export a surface mesh as a STL file

- added an option to the GEO output routine to save the surface mesh
  as discrete surfaces associated with the geometrical surfaces

- added STL and Text output formats for post-processing views (the
  text output allows for example to exploit plugin-generated data in
  gnuplot)

- generalized Plugin(Evaluate):

  * can loop automatically over all the timestep and/or components

  * can do operations using data from an external view

     - if the 2 views are based on the same grid, the plugin does the
       evaluation very efficiently

     - if the 2 views are based on differenet grids, the plugin
       automatically interpolates the external view data onto the
       grid of the current view

- added new Rand() function in MathEval

- default colormap is now # 2 (the Matlab "Jet" colormap)

Generalized the Levelset routines so that we can compute isovolumes with
all levelset-based plugins. This allows to extract either side of a
levelset (i.e., a half space with CutPlane, the interior/exterior of
a sphere with CutSphere, or the isovolume inside an isosurface with
CutMap).

- More intelligent way to detect if we need to apply a polygon offset
or not.

- better computation of translation coef in Draw2D

- On Mac, Cmd==Ctrl
- better menu dividers

Fixed all (well, most) string memory leaks in the parser. I've run
automated tests on all the demos and benchmarks, and I did not see
anything suspicious (no crashes, double frees, etc.)

******************************************************************
******************************************************************
*********** Pretty please, please give this version **************
*********** a try, especially on files with lots of **************
*********** loops, includes, arrays of variables,   **************
*********** etc., and report any problems. Thanks!  **************
******************************************************************
******************************************************************

fix tex output in gl2ps for large scenes

- cleaned up + generalized font selection
- generalized Plugin(Annotate) to allow font style selection for
  each text fragment
- fixed bug in per-view color selection

new Plugin(Remove) to selectively remove parts of a view (e.g., all
the text strings, all the scalar lines, etc.). Very useful to clean up
maps after cuts, or to reset comment strings.

- 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

- 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 colormaps (jet, hot and pink from Matlab) + generalized
  handling of grayscale colormap

- new View.Colormap option (this enables Gmsh to remember which
  colormap to use or which colormap the current modified colormap
  comes from) + better View.AlphaChannel treatment

- fix saving of color options when color_scheme is != 0

added File->Rename menu

nicer stippling patterns