ENH: Time: secondary write controls, signal handling

tutorials/incompressible/icoFoam/cavity/system/controlDict

@@ -31,6 +31,10 @@ writeControl    timeStep;
 
 writeInterval   20;
 
+//- Additional dump every hour of cpuTime for e.g. restarts
+//secondaryWriteControl    cpuTime;
+//secondaryWriteInterval   3600;
+
 purgeWrite      0;
 
 writeFormat     ascii;