Yes it is to be moved to dune-grid, but for the transition it is
easier to use the one from this module.

[[Imported from SVN: r9916]]

[[Imported from SVN: r9902]]

[[Imported from SVN: r9840]]

[[Imported from SVN: r9764]]

No idea why valgrind didn't complain about this.

[[Imported from SVN: r9758]]

[[Imported from SVN: r9749]]

And use it in one place in VectorCommunicator

[[Imported from SVN: r9748]]

[[Imported from SVN: r9733]]

[[Imported from SVN: r9732]]

Those do many-to-one communication with a single method call.
Previously, two subsequent calls were needed.  There is no reason
why the interface has to consist of two calls.  A single one is
much easier to use.

[[Imported from SVN: r9730]]

The globalindex.hh and uniqueentitypartition.hh is from Benedikt Oswald.
The rest is from Benjamin Bykowski, with a few fixes from me.

The globalindex stuff should go into dune-grid eventually, but it needs
some polishing first.

[[Imported from SVN: r9718]]