- 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

   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

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

fix position of BoundaryLayerPoints

- implemented all missing 2nd order representations
- removed unused member functions in GFace + cleaned up GFace::point

curvature control is ok
divide and conquer algo has been cleaned up

Plane surfaces are now recognized and the
usual gmsh "cross" is drawn correctly

prepare for extrusion