I'm hitting this too. I can't hard-code /usr/share/java/ant-contrib.jar in my build.xml because the project also needs to be built on non-Debian machines (that put ant-contrib.jar elsewhere) too.
I'm working around this by bundling the ant-contrib jar in my project so that I can reference it with a build.xml-relative path. -- To UNSUBSCRIBE, email to debian-bugs-dist-requ...@lists.debian.org with a subject of "unsubscribe". Trouble? Contact listmas...@lists.debian.org