Before running build.py, compile the special PyServlet classes:

CLASSPATH=$CATALINA_HOME/common/lib/servlet.jar:$JYTHON_HOME/jython.jar \
    javac classes/uk/org/boddie/webstack/util/PyServlet.java

Any supplied classes will have been produced by compiling the given source code
against libraries provided with the stated tested framework (see the main
README.txt document for details).
