[Dune] isLeaf method

[Christian Engwer]

Hi,

I can't remember the reasons. The isLeaf method is only available for
codim-0 entities. In case of higher codim entities, this method is not
there. Is there a specific reason for this behaviour? As there is no
way of accessing entities of lower codimension from those with higher
codimension, I don't see any way of getting the isLeaf information
without a complete grid loop.

Christian