The ant-<version>.jar is not being included in the distribution.
Integrated in Hadoop-trunk #640 (See http://hudson.zones.apache.org/hudson/job/Hadoop-trunk/640/)
I just committed this to trunk, branch-0.19 and branch-0.18.
+1 This looks right to me.
One line fix to include the ant jar. This renames the ant jar file from ant-$
-ant.jar which makes is consistent with the rest and will get it included into the tar file.