Qualify unqualified cout/endl in vtkPlusPolydataForce

vtkPlusPolydataForce.cxx used bare cout/endl, which relied on a transitive
using-directive that newer libc++ no longer provides, so it fails to compile
with "use of undeclared identifier 'cout'". Add a using directive so the file
builds. Independent of ITK/VTK version.

Author: hjmjohnson

src/PlusDataCollection/Haptics/vtkPlusPolydataForce.cxx

@@ -10,6 +10,8 @@ See License.txt for details.
 #include "vtkPolyData.h"
 #include "vtkPlusPolydataForce.h"
 #include "vtkMatrix4x4.h"
+
+using namespace std;
 
 //----------------------------------------------------------------------------