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

- 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 lc_extend_from_boundary in GUI

   1) this removes the asymmetry in all the routines involving mesh
      elements associated with points

   2) it makes it possible to use point-based datasets in the
      model-based post-processing module

  **********************************************************
    PLEASE TEST --- ESPECIALLY THE INPUT/OUTPUT ROUTINES!
  **********************************************************

* made GModel::getEntities() more efficient and generalized its use

  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

arghh, MED 2.3.3->2.3.4 changed the name of the enum MED_NOEUD_ELEMENT into
MED_NOEUD_MAILLE !

- separate setNode and tagNode in API

  integer tags per step data
- ported Eigenvectors and StreamLines plugins to the new post-pro API

- ported Gradient, Curl, Divergence, Integrate and Transform plugins
  to the new abstract post-pro API

- documented new post format

- replaced "Mesh.ContrainedBackgroundMesh" by "Mesh.CharacteristicLengthFromPoints" and
  "Mesh.CharacteristicLengthExtendFromBoundary"

- fixed MED IO when numComp > 9

- last thing missing is GaussPointData

- fix wrong vertex ordering in BDF