Copy the JARs in this directory into Ant's lib/ directory (i.e.,
$ANT_HOME/lib, the same directory where 'optional.jar', shipped with
Ant, lives).  The build system has been designed so that you needn't
do this to do basic development activities, but some build targets are
only functional if you perform this step.

See http://thdltools.sf.net/BuildSystems.html for more info.