TUT: simple test for redistributePar with distributed roots

TUT: prefer 'subtract' instead of old 'delete'

TUT: enable multiFieldValue function object, update topoSet action

tutorials/multiphase/overInterDyMFoam/rigidBodyHull/background/system/topoSetDict

@@ -53,7 +53,7 @@ actions
     {
         name    c1;
         type    cellSet;
-        action  delete;
+        action  subtract;
         source  cellToCell;
 
         set     c2;