moved most OS-dependent functions in OS.cpp

characteristic lenghts, that would lead to HUGE meshes (this is one
of the most common causes for erroneous bug reports on the mailing list)

remove obsolete BGM structure

removing dead code

rewrote the smooth normal routines:

- the averaging is now done by clusters, which is much better for
  geometries that have sharp edges  (it's a little slower, but the
  visual results are much better)
- there is now only a single smooth normal container in the mesh
  (instead of one per surface)

- new button under the graphic window to temporarily disable mouse
  selection (speeds-up redrawing of very large models + permits to
  rotate/zoom-in a model in selection mode even when the whole screen
  is full of selectable entities--e.g. a surface mesh)

- new "lasso" selection mode (to select entities using the same kind
  of lasso as the lasso zoom: just Ctrl+click, then drag the mouse in
  selection mode; the shortcuts are the same as for the lasso zoom)

- it is now possible to unselect entities using the middle mouse button
  (only for the creation of physicals at the moment; not sure if it's
  useful in the other cases)

- new button in visibility browser to invert the current selection
  (very useful e.g. when multiple physical entities are associated
  with a given elementary entity, in order to "peel" away the model
  when adding new physicals; cf. philou)

- changed meaning of Escape shortcut (cancel lasso or toggle mouse
  selection) + restore standard fltk Escape handling for all dialog
  windows

- updated copyright string

- new mesh label mode (coordinates); all label types are now also
  available for mesh vertices

- added option in 'Print Option' dialog to disable printing of help
  strings

- added a comment string with the date when creating a new file

- new snapping grid for adding points in the GUI

make it possible to add second order vertices for a mesh read from
a file (without cad)

use it now with -partition N for N partitions
only works with tets and triangles
output should be added (useless for now)

Removed the last bits of the "Discrete Surface/Line" stuff.

Gmsh can now simply read a .msh file, and use it as the boundary mesh
of a 3D mesh. For an example on how to do this, cf.
demos/sphere-discrete.geo.

This complements nicely the STL remeshing stuff: Gmsh can now
for example very easily be used to extrude surface meshes that
come from other tools.

make full-quad algo work for non-plane surfaces

fixed full-quadrangle recombine algo:

- run globally, not for each surface
- assign entities to elements
- split line meshes
- correctly re-tag vertices as 1st order
- plug memory leaks

add num of physical groups in stat window

polih previous commit

copyright update

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).

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.

Don't call Mesh_Quality() in GetStatistics()

added optimization hooks in the interface (GUI + comamnd line)

We can now use Netgen's optimization pass on our own Delaunay meshes. It seems
to work pretty well on small examples, but it definitely requires more
testing :-)

more fixes for netgen

Added hooks to optimize our meshes using netgen (in particular: the "special"
volume 99999 is now cleaned up after use and all the elements/vertices are
transfered back into the original volumes)

As a bonus, this finally allowed me to remove the ugly hacks in the volume
mesh drawing routines...

- mesh.algo -> algo2d and algo3d
- replaced most of the remaining radio buttons with Fl_Choices (requires
  less screen real estate)

- 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

Small corrections for ONFILE background meshes:

- should now work reliably interactively (and not only the first time
  the view is applied as a background mesh)

- fixed some memory leaks

- Added nice little buttons in the mesh menu to choose between 1st and
2nd order interactively

- Added 2nd order mesh stats in the GUI

- Fixed second order mesh generation in 3D (on simplices only at the moment).

- In prevision of the extension to hexas, prisms and pyramids, all elements
are now derived from a new Element base class, which will be used in the
generalization of Edge/EdgesContainer in the future.