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

removed parFromPoint and closestPoint from GEdge; replace their use in
cgns code by appropriate reparamMeshVertex calls (not tested: I don't have
cgns)

removed now unused golden section minimizer (brent), now unused

There's no new functionality for now: PLEASE TEST THAT EVERYTHING
WORKS AS IT USED TO BEFORE.

- removed every "throw;", i.e., every throw that did not throw an actual exception.
  throw wihout args should ONLY be used in a catch{} to re-throw the same exception
  (for it to be handled in another catch clause)

- introduced GmshMessage callback class so that clients can easily implement
  their own message handling (see example in driverOCC.cpp)

  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

untabify

API cleanup: removed unused functions

	-) A bug has been corrected in the MeshAdapt Procedure
	-) The 2D Delaunay is now Anisotropic
	-) 3D Sliver removal procedure has been improved
	-) Curvilinear mesh generation has been slightly improved,
	   even if it is still far from done
JFR

make clear in docs that node/elemement tags should be > 0 (and not == 0)

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

set min num pts=2 for OCC circles (fixes bug in Mblade.iges)

- reimplemented subdivision of extruded meshes
- fix indent + unused var + gcc warnings all over the place