BUG: parallel blocking with faFieldDecomposer, faMeshReconstructor (fixes #2237)

- the patch remapping in faFieldDecomposer calls weights
  internalField() which can trigger parallel communication on the
  complete mesh for some processors only (ie, blocks).

  Force a priori creation of weights instead.

- ensure that the complete mesh (reconstruction helper)
  is serial when adding patches.

src/parallel/reconstruct/faReconstruct/faMeshReconstructor.C

@@ -517,7 +517,13 @@ void Foam::faMeshReconstructor::createMesh()
         );
     }
 
+    // Serial mesh - no parallel communication
+
+    const bool oldParRun = Pstream::parRun(false);
+
     completeMesh.addFaPatches(completePatches);
+
+    Pstream::parRun(oldParRun);  // Restore parallel state
 }