Went through the process a couple more times at home, and I have some questions still to be answered, and some additions to the script:

When it got to this line:

apt-get remove `apt-cache search gcj | grep gcj | awk '{print $1}'`

apt reported that it was uninstalling jing. I'd previously been puzzled about the absence of jing at the end of the script, because it's explicitly installed before this point, but it looks like this is the reason. I'm just wondering what that line is actually doing. I got it from the wiki:

and it looks like SY added that line in July last year:

http://wiki.tei-c.org/index.php?title=TEIDebian&diff=7877&oldid=7875

I can add another line to my script to reinstall jing, so it's no problem, but I've written to ask him why he did that. Perhaps it's not necessary to remove all that stuff, because installing jing just brings a lot of it back anyway.

If we don't delete that stuff, the addition would be:

echo "Reinstalling jing, which just got removed by the previous line."
apt-get install jing

We can also restart Jenkins at the end of the script, so the user doesn't have to:

echo "Restarting Jenkins server, so that it finds and initializes all the new plugins."
/etc/init.d/jenkins restart