SAXON: Fatal Error! Cannot find a matching 1-argument function named {http://exslt.org/common}node-set(). There is no Saxon extension function with the local name node-set

I was working on a DITA-OT plugin when I encountered this guy:

Fatal Error! Cannot find a matching 1-argument function named {http://exslt.org/common}node-set(). There is no Saxon extension function with the local name node-set

I am using the latest version of SAXON HE which apparently does not support EXSLT.
http://www.saxonica.com/feature-matrix.html
However you can pay $50 bucks or more for the PE and EE versions. Or you can save yourself some green and download SAXON 9.1.0.8 which was the last version to support EXSLT. You can download the JAR file here and put it on your classpath. Hint: The download link is next to the floppy drive icon.
Download saxon-9.1.0.8.jar

For a DITA project you'll also need the following jar:
Download saxon-dom-9.1.0.8.jar

And if you are using Eclipse you can set the classpath by doing the following:

1. On the file menu click: Window > Preferences > Ant > Runtime > Classpath tab > Global entries
2. Remove the existing versions of SAXON from the classpath
3. Click the "Add External Jars" button
4. Add "saxon-9.1.0.8.jar" and "saxon-dom-9.1.0.8.jar"