Remove dependencies on TGraph.h and TH1.h

git-svn-id: http://root.cern.ch/svn/root/trunk@17466 27541ba8-7e3a-0410-8455-c3a389f83636

tmva/inc/PDF.h

-// @(#)root/tmva $Id: PDF.h,v 1.10 2006/11/20 15:35:28 brun Exp $
+// @(#)root/tmva $Id: PDF.h,v 1.11 2006/11/23 17:43:38 rdm Exp $
 // Author: Andreas Hoecker, Joerg Stelzer, Helge Voss, Kai Voss 
 
 /**********************************************************************************
@@ -38,14 +38,16 @@
 //                                                                      //
 //////////////////////////////////////////////////////////////////////////
 
-#include "TSpline.h"
-#include "TH1.h"
-#include "TGraph.h"
+#include "TObject.h"
 
 #ifndef ROOT_TMVA_MsgLogger
 #include "TMVA/MsgLogger.h"
 #endif
 
+class TH1;
+class TGraph;
+class TSpline;
+
 namespace TMVA {
 
    class PDF : public TObject {