virtual to enable inheritance.
09-feb-2003 NvE Class AliCalcluster derived from AliSignal to enable automatic signal setting
for various rings of modules around the cluster center.
+10-feb-2003 NvE Class AliSignal modified such that also signals without errors can be stored.
+ This may minimise memory occupation and output file size.
+18-feb-2003 NvE Memberfunction ShowCalorimeters() introduced in AliEvent to display an overview of all
+ available calorimeter systems.
+ Date/time format changed and ShowCalorimeters() invoked in AliEvent::HeaderData().