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)

moving to new post-processing database

                    *** WARNING ***

do not upgrade if you need plugins or adaptive views: these have not
been ported (yet) to the new database

                    *** WARNING ***

added simple boundary operator in parser

add bit of code to intersect curves with a surface (allows to do "poor man's"
trimmed patches ;-)

small cleanups for 2.0.8

tCircle and tCoherence were removed from the lexer? WTF?

background mesh. I've still to write some fields sub-class, but backward
compatibility should be ok now.
Jonathan
----------------------------------------------------------------------

- boundary layer can now be generated by using a post-pro view for the
  normal field

- added more operations on lists in parser (FExpr * FExpr_Multi, etc.)

- new "hole carving" code to create extruded grids carved out around
  some surfaces (the resulting cavity can be filled with "grout" using
  the unstructured algos)

- check if bboxes of post-pro views are not == VAL_INF before adding
  them to the model bbox (bug report from Renaud Sizaire)

- fixed crash in LCM_xxx tensor drawing code when no tensor points are
  available. (This piece of code should be cleaned up further--no time
  for that now.)

- generalize Levelset plugins so that they work on point data sets

corrected some bugs in 2d mesher & occ interface

- save physicals labels when saving unrolled geometries
- fixed crash in unrolled geo save (discrete points)
- Delete Physicals now also deletes the physicals in GModel
- removed unused rules and terminals in parser
- put at least one mid-point when meshing non-straight lines
  in OCC: this fixes most of the trivial 2d meshing problems

removed most unused, untested or non-working stuff in old CAD code

new option to compute char lengths from curvature + removed most unused mesh options