Hmm.. I am afraid you will need to do it that old fashioned way. Detect a focus change event, then check with your recorded X,Y, if the same, it is a window move start and on the next focus change event, that is the window move end...
I tried signal_connect to all these other events: http://gtk2-perl.sourceforge.net/doc/gtk2-perl-tut/sec-Events.html They do not give anything for window...