Fix extending the PackagerBase from another jar

In case we have:
			<plugin>
				<groupId>org.codehaus.izpack</groupId>
				<artifactId>izpack-maven-plugin</artifactId>
				<executions>
					...
				</executions>
				<configuration>
					...
				</configuration>
				<dependencies>
					<dependency>
						<groupId>group</groupId>
						<artifactId>artifact</artifactId>
						<version>version</version>
					</dependency>
				</dependencies>
			</plugin>
And in this dependency we have some class for extending the PackagerBase - we unable to build setup.jar.