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

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)

SyncModel to force transfer from old GEO db to GModel

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

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

allow recombine, transfinite and embedding constraints on GModel entities
in parser

- 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

****************************************************************
**** PLEASE TEST YOUR SCRIPTS (ESPECIALLY ONES WITH LISTS, *****
****        COMPLICATED AFFECTATIONS, ETC.)                *****
****************************************************************

* removed unused stuff (more to come)
* moved remaining into Common

  did in high
* added mesh generation error log summary
* removed Parallel subdir (this is now handled by the message class)
* removed Box subdir and consolidated batch processing in a single
  routine
* made List_T into a class
* reduced dependencies in Pview*.h so we can eventually add the post-pro
  interface to the public API

re-fix Field.h API dependency

fix shift/conflict reduce in parser introduced by Field stuff

api cleanup: use ByTag consistently (emphasises slowness of lookup)

Smoother Surface{list} = numsteps;

make parser embeddable in code with other parser (yy->gmsh_yy)
more work on headers
fixed lots of gcc warnings

start reducing header pollution (removed Gmsh.h + cleaned up GModel & co)

fix parser to work with new flex and bison (1.28 -> 2.3)