Add qualifier to enflux function

With this qualifier the normalization value can be retrieve.
This is useful to calculate the flux of components

src/fitting/fit-functions/enflux.sl

@@ -4,6 +4,11 @@ private define enflux_fit(lo, hi, par, y)
 %!%+
 %\function{enflux (fit-function)}
 %\synopsis{fits the photon flux in a given energy range}
+%
+%\qualifiers{
+%    \qualifier{norm}{If given a reference to a variable, store the
+%                     normalization factor in there.}
+%}
 %\description
 %    This function can be used as a convolution model to determine
 %    the energy flux [keV/s/cm^2] of the model in the energy range
@@ -65,12 +70,21 @@ private define enflux_fit(lo, hi, par, y)
   variable flux = par[0];
   variable l1 = _A(par[2]);
   variable l2 = _A(par[1]);
+
+  variable norm_value;
+  variable store_norm = qualifier("norm");
+
   if (Fit_Verbose >= 0 && (l1 < lo[0] or l2 > hi[-1]))
     vmessage("warning: enflux energy range (%.2e-%.2e keV) not covered by data grid (%.2e-%.2e keV)",
 	     par[1],par[2],_A(hi[-1]),_A(lo[0]));
   variable i = where(l1 <= lo and hi <= l2);
   variable mean_e = _A(1.)/(0.5*(hi+lo)[i]);
-  return y * flux / sum( mean_e*y[i] );
+  norm_value = sum( mean_e*y[i] );
+
+  if (typeof(store_norm) == Ref_Type)
+    @store_norm = norm_value;
+    
+  return y * flux / norm_value;
 }
 
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