make --nan-equal an argument for acmd diff-root, use it for frozen derivation tests

Tools/PyUtils/python/scripts/diff_root_files.py

@@ -89,6 +89,11 @@ default='%(default)s'.
 allowed: %(choices)s
 """
                   )
+@acmdlib.argument('--nan-equal',
+                  action='store_true',
+                  default=False,
+                  help="""Compare nan as equal to nan""")
+
 def main(args):
     """check that 2 ROOT files have same content (containers and sizes)
     """
@@ -280,7 +285,7 @@ def main(args):
                 tree_name, jentry, name, inew = d_new
 
             # for regression testing we should have NAN == NAN
-            if isnan(iold) and isnan(inew):
+            if isnan(iold) and isnan(inew) and args.nan_equal:
                 n_good += 1
                 continue