[hist] add missing includes

Fixes compiler warnings about using incomplete type

[hist] add missing includes

Author: silverweed

hist/unfold/src/TUnfold.cxx

@@ -108,6 +108,7 @@ constraint, both x and λ are determined.
 */
 
 #include <iostream>
+#include <TGraph.h>
 #include <TMatrixD.h>
 #include <TMatrixDSparse.h>
 #include <TMatrixDSym.h>

hist/unfold/src/TUnfoldDensity.cxx

@@ -153,6 +153,7 @@ final choice of tau should sit right in the minimum</li>
 */
 
 #include "TUnfoldDensity.h"
+#include <TGraph.h>
 #include <TMath.h>
 #include <TVectorD.h>
 #include <TObjString.h>

hist/unfold/src/TUnfoldIterativeEM.cxx

@@ -1,6 +1,7 @@
 #include "TUnfoldIterativeEM.h"
 #include "TUnfoldBinning.h"
 #include <TVectorD.h>
+#include <TGraph.h>
 
 ClassImp(TUnfoldIterativeEM)