control: Restore MPI_THREAD_MULTIPLE removed by !282 as SERIALIZED seems to be...

control: Restore MPI_THREAD_MULTIPLE removed by !282 as SERIALIZED seems to be insufficient to manage the datatypes

control/control.c

@@ -102,12 +102,12 @@ int __chameleon_initpar(int ncpus, int ngpus, int nthreads_per_worker)
            * In testings, only StarPU's internal thread performs
            * communications, and *then* Chameleon performs communications in
            * the check step. */
-          const int required = MPI_THREAD_SERIALIZED;
+          const int required = MPI_THREAD_MULTIPLE;
           if ( MPI_Init_thread( NULL, NULL, required, &provided ) != MPI_SUCCESS) {
              chameleon_fatal_error("CHAMELEON_Init", "MPI_Init_thread() failed");
           }
           if ( provided < required ) {
-             chameleon_fatal_error("CHAMELEON_Init", "MPI_Init_thread() was not able to provide the requested thread support");
+             chameleon_fatal_error("CHAMELEON_Init", "MPI_Init_thread() was not able to provide the requested thread support (MPI_THREAD_MULTIPLE), this may be an issue if the level provided is not enough for the underlying runtime system.");
           }
       }
     }