Typedef return type from TSpectrum

Fixes #18

NPLib/Calibration/NPSiliconCalibrator.cxx

@@ -8,6 +8,13 @@ using namespace std;
 #include "TSpectrum.h"
 #include "TH1.h"
 
+namespace {
+#if ROOT_VERSION_CODE > ROOT_VERSION(6,0,0)
+  typedef Double_t* TSPECTRUM_RETURN;
+#else
+  typedef Float_t* TSPECTRUM_RETURN;
+#endif
+}
 
 NPL::SiliconCalibrator::SiliconCalibrator(){
 }
@@ -213,7 +220,7 @@ TGraphErrors* NPL::SiliconCalibrator::FitSpectrum(TH1* histo, double rmin, doubl
    TSpectrum* sp = new TSpectrum(4,1);
    //  nfound = sp->Search(histo,3,"",0.25);
    Int_t    nfound = sp->Search(histo,3,"",0.5);
-   Float_t* xpeaks =(Float_t*) sp->GetPositionX();
+   TSPECTRUM_RETURN xpeaks = sp->GetPositionX();
 
    // order list of peaks
    sort(xpeaks, xpeaks+nfound);