Restricted integration to interior elements

This avoids summing up elements twice when using the integrate() function in parallel with overlapping grids.

src/amdis/Integrate.hpp

@@ -2,6 +2,7 @@
 
 #include <type_traits>
 #include <dune/geometry/quadraturerules.hh>
+#include <dune/grid/common/partitionset.hh>
 #include <amdis/GridFunctions.hpp>
 
 namespace AMDiS
@@ -17,7 +18,7 @@ namespace AMDiS
       using Range = typename GridFct::Range;
       Range result(0);
 
-      for (auto const& element : elements(gridView)) {
+      for (auto const& element : elements(gridView, Dune::Partitions::interior)) {
         auto geometry = element.geometry();
 
         localFct.bind(element);