Add include guard to vtkPythonCompatibility.h

Wrapping/PythonCore/vtkPythonCompatibility.h

@@ -16,6 +16,8 @@
   This header contains macros to make Python 2 and Python 3 play nice.
   It must be included after vtkPython.h.
 -----------------------------------------------------------------------*/
+#ifndef vtkPythonCompatibility_h
+#define vtkPythonCompatibility_h
 
 // define our main check macro VTK_PY3K
 #if PY_MAJOR_VERSION >= 3
@@ -128,3 +130,4 @@ typedef struct bufferinfo { PyObject *obj; } Py_buffer;
 #endif
 
 #endif
+#endif