* this way one can call as_imp() when matching against an interface

* not sure if gcc and icc understand this

so we get the have_module macro for it

* to avoid clashes with Dune::Exception

* according to Rene

* this defines CHECK_CRTP and CHECK_AND_CALL_CRTP
  (has still to be made threadsafe perhaps?)
* defines CRTPInterface

* there is now DUNE_THROW_COLORFULLY :)

* copyright decision still open

* we still need to decide if we want to have project wide
  copyright holders (if yes, who?) or per-file

* use one template which either redirects scalars to
  dune-common and checks vectors componentwise
* this template is then generated for eq, ne, gt, lt, ge and le