* 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

shoot yourself in the foot with this: use with caution!)

Options/GUI for partitioning software

- don't play tricks in Extend1DMesh & co: always follow the option (so we
  can predictbly mix point/curvature lcs with fields)

orientation in extrusions

INRIA input corrected and enhanced

- 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)