[Dune] boundaryIndex on coarse grid

[Christian Engwer]

While updating the strcutured grids, I was wondering about a small
detail in the boundaryIndex interface.

The meeting minutes state:

The user must be able to attach boundary information to the level-0
boundaries.
   1. Up to now the boundaryIDs allowed to associate an int with a
	  boundary segament.
   2. The new proposal is to have an index with a boundary index. This
	  is (more) consistent with the other indicies and allows to
	  associate more or less any data with boundaries. The number
	  would be inherited from the coarse grid.

It does not say anything about the number of indices on the coarse
grid. I also thought, that that was the purpose of the
numBoundarySegments method.

These descriptions especillay allow to have a boundary segment that
covers several coarse grid element, like the whole left side on a
strcutures grid. The gridcheck on the other hand complains.

So my question now is.

* What is the desired feature. Do we allow "multielement"-segments?

Christian