[Dune] ISI final suggestion:

[Andreas Dedner]

I want to suggest, to change the interface
as given below. It seems to me that we can manage
this for 1.0, so I will change the interface
at the beginning of next week if I don't get any
negative feedback.
New interface:

Dune Entity Class:
  IntersectionIterator ibegin () const DUNE_DEPRECATED
    {
      return realEntity.ibegin();
    }
  IntersectionIterator iend () const DUNE_DEPRECATED
    {
      return realEntity.iend();
    }
  LevelIntersectionIterator libegin () const
    {
      return realEntity.libegin();
    }
  LevelIntersectionIterator liend () const
    {
      return realEntity.liend();
    }
  LeafIntersectionIterator leafibegin () const
    {
      return realEntity.leafibegin();
    }
  LeafIntersectionIterator leafiend () const
    {
      return realEntity.leafiend();
    }