Workaround a problem with x2go and gnome-session.
The resolution set by x2go is not honored by gnome-session,
so set it explicitly with xrandr.  Note that this code has one line of
perl, and I am adding perl as a dependency to puavo-ltsp-client.
(I think the perl call could be replaced by almost as good a ruby call,
but I do not bother and besides, this package does have a hidden
dependency to perl anyway, so make that explicit for now).