basetrans was not updated before computing the real coordinates, thus
leading to invalid rectangles

This is needed to get sdlisting updated before checking it in the echo
condition.

get_eta could be called from statuschecker thread after self.p.printing
was set to True but before startcb was called in print thread, thus
leaving compute_eta uninitialized

Update readme to include info on Chrome OS #536

Not all debian derivatives pull in dbus and psutil by default (eg crouton trusty target)