Protect window objects from GC in gtk.window_get_toplevels()
Protect window objects from GC in gtk.window_get_toplevels()

Fixes bug #574259.

amremam2004/pygtk,amremam2004/pygtk,GNOME/pygtk,Distrotech/pygtk,Distrotech/pygtk,amremam2004/pygtk,nzjrs/pygtk,nzjrs/pygtk,Distrotech/pygtk,GNOME/pygtk,nzjrs/pygtk,GNOME/pygtk