TriangleBSPT: fix preprocessor guard, avoid unnecessary forward declaration.

libs_required/ACG/Geometry/bsp/TriangleBSPT.hh

@@ -222,13 +222,8 @@ public:
 };
 
 
-#ifdef ENABLE_OPENVOLUMEMESH
-
-namespace OpenVolumeMesh {
-    class VertexHandle;
-    class FaceHandle;
-}
-
+#ifdef ENABLE_OPENVOLUMEMESH_SUPPORT
+#include <OpenVolumeMesh/Core/PropertyHandles.hh>
 //== CLASS DEFINITION =========================================================
 
 // Make sure all faces of the mesh have valence 3.