Don't let Matthieu do python stuff unsupervised.

tools/task_plots/plot_tasks.py

@@ -412,7 +412,7 @@ sdata = sdata[sdata[:, toccol] != 0]
 
 if delta_t < 0.:
     print("The time-range must be >=0!")
-    return 1
+    sys.exit(1)
 # Each rank can have different clocks (compute node), but we want to use the
 # same delta times range for comparisons, so we suck it up and take the hit of
 # precalculating this, unless the user knows better.