Clean-up & small syntax change for homology commands.

Added parser interface for homology computation (finally).
A tutorial will follow.

renamed most gmsh* classes

better pre-fill of solver fields in GUI

stuff, like plugin drawing

Encapsulate toolkit-dependent global drawing functions in new
drawContextGlobal class, and add a static drawContextGlobal to
drawContext, with a default version that does nothing.

This allows to have a completely virtualized drawing system: we can
now ship a library with a fully working graphic system, indepedent of
the widget toolkit. A client code just needs to subclass
drawContextGlobal to get working graphics (see
e.g. api_demos/mainAntTweakBar.cpp)

levelset from postview !

add matheval levelset

more work on levelsets & co

re-committing work from last two days after server crash:

- refactored old Geo code (new/delete)
- moved DrawPlugin to Plugin
- move from matheval to mathex
- move from Flu_Tree_Browser to Fl_Tree
- fixed crash in Triangulate plugin

- moved GUI to FlGui + added experimental QGui to test Qt

- fixed most MSVC and gcc compiler warnings

- converted some remaining tabs to whitespace (that's why the patch is
  so large; please try to remember to indent with 2 spaces and not
  tabs when you commit stuff to CVS)

- merged modified patch from Konstantinos Poulios to allow saving
  physical/partition as element tags in mesh formats that don't
  support them natively

SyncModel to force transfer from old GEO db to GModel

fix STL export of quads

- replaced old 2nd order views with new adaptive stuff (still missing
  some function spaces for quads/hexas)

Emilie: added functions to remesh a volume

  the .msh format -> bumped version from 2.0 to 2.1)
- move createTopologyFromMSH into GModel.cpp (and renamed to
  createTopologyFromMesh)

added createTopology when Merging a MSH File and implemented discreteEdge