Make sequential repartitioning computation the default.

[[Imported from SVN: r1463]]

dune/istl/repartition.hh

@@ -954,7 +954,7 @@ namespace Dune
           std::cout<<"Creating comm graph took "<<time.elapsed()<<std::endl;
         time.reset();
 
-#ifndef SEQUENTIAL_PARTITION
+#ifdef PARALLEL_PARTITION
         float ubvec = 1.15;
         int ncon=1;