Do cleanup /images/image_update.stats.tmp.
On puavo-client-updater-applet, now things appear to work,
meaning "check for updates" and "progress bar" work okay
(I think).  But there is still quite a bit of polishing to do...
Put /usr/lib/puavo-ltsp-install/update-images in
puavo-client-daemon to a separate thread.
Some stylistic changes to puavo-client-updater-applet.
Progress bar stuff in puavo-client-updater-applet actually work now.