Note: As a side effect, the iterator test triggers an error in the edge
iterator of a 2d grid. Here, not all entities are visited.

grids seems not to work.

The only load-balancing algorithm useable without Zoltan is based on a
space filling curve. Internally, however, this algorithm assumes that
the macro elements are already sorted along such a curve. Originally,
this was ensured by sorting them along the Hilbert curve provided by
Zoltan.  To make dune-alugrid useful without Zoltan, we still need a
space filling curve implementation of our own.

This patch makes dune-alugrid more self-contained by providing a simple
implementation of a Z curve. It is used only when Zoltan is not found,
so experienced users will not notice the difference.

remove trailing white spaces from iterator.hh

additionally the codim number is still unique but will not overflow ever