Check for MPI 2 functionality and activate it for DUNE.

This allow mixing the MPIHelper and MPI_Init/MPI_Finalize. This commit
makes OPM a bit more DUNE compatible.

cmake/Modules/Finddune-common.cmake

@@ -57,6 +57,7 @@ int main (void) {
   HAVE_NULLPTR;
   HAVE_STATIC_ASSERT;
   HAVE_SHARED_PTR;
+  MPI_2;
   SHARED_PTR_HEADER;
   SHARED_PTR_NAMESPACE;
   HAVE_TYPE_TRAITS;
@@ -66,6 +67,15 @@ int main (void) {
   ")
 #debug_find_vars ("dune-common")
 
+# check for MPI version 2
+include(CMakePushCheckState)
+include(CheckFunctionExists)
+cmake_push_check_state()
+set(CMAKE_REQUIRED_LIBRARIES ${CMAKE_REQUIRED_LIBRARIES};${MPI_CXX_LIBRARIES})
+set(CMAKE_REQUIRED_INCLUDES ${CMAKE_REQUIRED_INCLUDES};${MPI_CXX_INCLUDES})
+check_function_exists(MPI_Finalized MPI_2)
+cmake_pop_check_state()
+
 # make version number available in config.h
 include (UseDuneVer)
 find_dune_version ("dune" "common")