Fix various issues with MPI and partitioning

These are two bugs and one feature in the current handling of repartitioning and MPI tasks.

Extracted from current developments so they do not get lost.

src/partition.c

@@ -383,9 +383,8 @@ static void pick_metis(struct space *s, int nregions, int *vertexw, int *edgew,
   /* dumpMETISGraph("metis_graph", idx_ncells, one, xadj, adjncy,
    *                weights_v, NULL, weights_e);
    */
-
-  if (METIS_PartGraphKway(&idx_ncells, &one, xadj, adjncy, weights_v, weights_e,
-                          NULL, &idx_nregions, NULL, NULL, options, &objval,
+  if (METIS_PartGraphKway(&idx_ncells, &one, xadj, adjncy, weights_v, NULL,
+                          weights_e, &idx_nregions, NULL, NULL, options, &objval,
                           regionid) != METIS_OK)
     error("Call to METIS_PartGraphKway failed.");
 
@@ -520,11 +519,7 @@ static void repart_edge_metis(int partweights, int bothweights, int nodeID,
     struct task *t = &tasks[j];
 
     /* Skip un-interesting tasks. */
-    if (t->type != task_type_self && t->type != task_type_pair &&
-        t->type != task_type_sub_self && t->type != task_type_sub_self &&
-        t->type != task_type_ghost && t->type != task_type_kick1 &&
-        t->type != task_type_kick2 && t->type != task_type_timestep &&
-        t->type != task_type_drift_part && t->type != task_type_drift_gpart)
+    if (t->cost == 0)
       continue;
 
     /* Get the task weight. */