ALUs comm.

This led to problems for example with choosing the right constructor
for GridFactory("name")

Merge branch 'paramerge' of https://users.dune-project.org/repositories/projects/dune-alugrid into paramerge

1) the dgf base class was not passing the communicator on to the grid factory
2) due to a default parameter the protected constructor was used when passing a
   communicator to the factory - removed default parameter seems to not cause any
   problem

length.

Problem is that with surface grids two elements can have the same barycenter and
would have only been added once into the map leading to missing elements in the grid
construction. Using a multimap is probably not the best solution since elements with the
same barycenter would be sorted to lie directly next to each other but probably they are
on opposite sides of the surface. Since will not lead to a good partitioning...

Merge branch 'paramerge' of https://users.dune-project.org/repositories/projects/dune-alugrid into paramerge