upgrade xfce?

Add ppa:xubuntu-dev/xfce-4.10.Try ppa:xubuntu-dev/xfce-4.12 if you want the beta. (NOTE: FOR ppa:xubuntu-dev/xfce-4.12 YOU NEED ppa:xubuntu-dev/xfce-4.10 FIRST!)

https://trisquel.info/en/forum/xfce

You may need to patch a package. This is an updated script for doing that.

#!/bin/sh

cd /tmp/
mkdir build-trisquel-desktop-common-data
cd build-trisquel-desktop-common-data/
# install build dependencies
sudo apt-get build-dep trisquel-desktop-common-data -y
# get package source (without sudo)
apt-get source trisquel-desktop-common-data
# get patch for removing package
wget https://trisquel.info/files/issues/ignore-errors.patch
cd trisquel-desktop-common-data-6.0/
# apply patch
patch debian/postrm ../ignore-errors.patch
# remove file
rm data/etc/xdg/autostart/xscreensaver.desktop -f
# build deb package
dpkg-buildpackage -uc -us
cd ..
# install the package
sudo dpkg -i trisquel-desktop-common-data_6.0-*_all.deb
cd ..
rm -rf build-trisquel-desktop-common-data/

What's the license for the script?

I think it is too small and simple to be needing a license (you can just read it and rewrite it easily). That being said, you can use it under GPLv3.