prebuilt_jar fails when the jar has duplicate entries in it.

Created by: rbraunstein

BUILD FAILED: //third-party/jmdns-3.4.0-jenkins-3-jar:jmdns-3.4.0-jenkins-3-jar failed on step get_class_names Optional.of(third-party/jmdns-3.4.0-jenkins-3-jar/jmdns-3.4.0-jenkins-3.jar) > buck-out/gen/third-party/jmdns-3.4.0-jenkins-3-jar/jmdns-3.4.0-jenkins-3-jar.classes.txt with an exception: Multiple entries with same key: com/strangeberry/jmdns/tools/Browser=903578aa54046efcab5fde9f4b5f229155897dac and com/strangeberry/jmdns/tools/Browser=903578aa54046efcab5fde9f4b5f229155897dac

In this jar, some classes are duplicated: http://maven.jenkins-ci.org/content/repositories/releases/org/jenkins-ci/jmdns/3.4.0-jenkins-3/

% jar -tvf ~/Downloads/jmdns-3.4.0-jenkins-3.jar | grep Browser 709 Tue Aug 09 13:24:14 PDT 2011 com/strangeberry/jmdns/tools/Browser$1.class 713 Tue Aug 09 13:24:14 PDT 2011 com/strangeberry/jmdns/tools/Browser$2.class 711 Tue Aug 09 13:24:14 PDT 2011 com/strangeberry/jmdns/tools/Browser$3.class 950 Tue Aug 09 13:24:14 PDT 2011 com/strangeberry/jmdns/tools/Browser$ServiceTableModel.class 6297 Tue Aug 09 13:24:14 PDT 2011 com/strangeberry/jmdns/tools/Browser.class 709 Tue Aug 09 13:24:14 PDT 2011 com/strangeberry/jmdns/tools/Browser$1.class 713 Tue Aug 09 13:24:14 PDT 2011 com/strangeberry/jmdns/tools/Browser$2.class 711 Tue Aug 09 13:24:14 PDT 2011 com/strangeberry/jmdns/tools/Browser$3.class 950 Tue Aug 09 13:24:14 PDT 2011 com/strangeberry/jmdns/tools/Browser$ServiceTableModel.class 6297 Tue Aug 09 13:24:14 PDT 2011 com/strangeberry/jmdns/tools/Browser.class