build-single.xml: outdated dependencies for opencms tasks

`ant-opencms-1.1.jar` is outdated. Current `ant-opencms-1.2.jar` pulls dependencies from `commons-digester-1.8.jar`, `commons-collections-3.2.1.jar`, `commons-logging-1.1.1.jar`, `commons-beanutils-1.8.0.jar`. The taskdef:

    <taskdef resource="org/opencms/util/ant/taskdefs.properties" loaderref="opencms">...</taskdef>

should be fixed accordingly.