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

* 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 :)

* 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

* LA::VectorInterface
* LA::EigenDenseVector

* rename DSC_TOSTR -> DSC_FRSTR
* group toString/fromString