- 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)

- merge OCC64 patch from Jose Paulo Moitinho de Almeida

* removed unused stuff (more to come)
* moved remaining into Common

"ParametricSurface" (not Plane)

- log vector scaling (idea from bernhard Kubicek)