fixed newton in DG

in GUI to avoid flood of messages on mailing list (thx to Dave for this)

with other toolkits than fltk

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

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

HAVE_XXX defines.

This fixes three longstanding problems:

- the API was hard to use because some headers had HAVE_XXX ifdefs, so
  that cient codes had to know how the lib was compiled to compile
  themselves

- we had to do make clean after each ./configure, which erased too
  much (e.g. most of contrib)

- make depend could include unwanted stuff since it redefined FLAGS

- fix bb computation to avoid model jumping around when adding points in z=0 plane
- pass interpol matrices as ref

in-house of blas/lapack)

- fixed missing getShapeFunction/getGradShapeFunction + return all sf
  at once so we can implement MElement in term of these consistently
  (w or w/o FunctionSpace)

- can now merge multiple meshes and remove duplicate mesh vertices
  (useful e.g. when merging several STLs)

- added easy interface to create model-based postpro datasets on the
  fly + use this for mesh quality stats

add string.h needed for strdup and strcmp with some gcc version

geom entities