sampledSurface hacking proof-of-concept

- using 'nil' type to write geometry only, in the future we could fallback to 'null'
  writer and hook in arbitrary formats from surfMesh

- IOobject gets writeEndDivider() static method

src/conversion/meshReader/meshReaderAux.C

@@ -97,10 +97,8 @@ void Foam::meshReader::writeInterfaces(const objectRegistry& registry) const
     OFstream os(ioObj.objectPath());
     ioObj.writeHeader(os);
 
-    os  << interfaces_
-        << "// *************************************"
-        << "************************************ //"
-        << endl;
+    os << interfaces_;
+    io.writeEndDivider(os);
 }