[Seaside] how to determine server is inactive

[Yanni Chiu]

I would like to have a Seaside image automatically save&quit, if it is 
inactive. Now, how should the inactive state be determined?

IIRC, in Seaside-2.8 you could scan the WASession instances and look at 
a timestamp that each instance held. The WACache stuff in Seaside-3.0 
looks very different. Should I scour the WACache usage, to figure out 
whether the server is inactive (i.e. not handled any requests recently, 
or alternatively, all sessions have expired)? Or, is there some other 
simple way to know that the server is inactive.