The Wrapper classes were removed because of to high maintanace overhead.
There are only two implementation classes now,
GatherScatterLoadBalance and GatherScatterLoadBalanceDataHandle.

more cleanup to come.

used to move data during load balancing. The dune-fem DofManager has been adjusted
accordingly.

- instead of #ifndef NDEBUG
  now use #ifdef ALUGRIDDEBUG
- istead of assert( cond );
  now use alugrid_assert ( cond );
  (from dune/alugrid/common/alugrid_assert.hh)
So instead of having to define NDEBUG to avoid debug code being executed
(improves performance by 60%) one always avoids debug code as long as
ALUGRIDDEBUG has not been define.

  MPI_Comm --> ALUGridMPIComm
  No_Comm  --> ALUGridNoComm

Now the library compilation yields always the same result, independent of HAVE_MPI.
Also, almost all ALU3DGRID_PARALLEL could have been removed.
From now on, there should be no .cc file containing ALU3DGRID_PARALLEL or HAVE_MPI.
Otherwise it must be an inline header file.