Adds an option to switch elementary and physical tags in loaded meshes, and fixes a bug with geo-mesh matching.

(which use the filename to guess which data file to read). Laurent's patch would set 
the filename to the last merged file, whereas we currently want the file name to be 
set to the projet file, i.e., the first merged file.

We should maybe think a bit harder about how to deal with this (maybe each Merge can 
set the fileName, but OpenFile takes precedence?)

* issue error for zero volume elements in FEA export
* reset element number between 2D/3D in FEA export

- partial fix for skipping empty time steps

 bar: it's not dynamic in fltk 1.1)

- invert #define logic (HAVE_MESH, HAVE_POST, HAVE_SOLVER, ... instead of HAVE_NO_MESH,
  HAVE_NO_POST, HAVE_NO_SOLVER)

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)

GModel::readGEO must be a static member function, since the parser can
now create multiple models!

more work on levelsets & co

- 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

fix STL export of quads

Added a sort of the eigenvalues and print functions

added createTopology when Merging a MSH File and implemented discreteEdge