ant tar should package contrib jars

From Hadoop-356:
>I note that the contrib packages are not included in distributions (the "tar" target).
>They probably should be. Michel, would you like to modify "tar" to include the contrib code?
>This should be done in a separate bug.

OK.
This packaging is done in target deploy-contrib.
So I can just add a dependency to the top-level tar target:
<!-- Make release tarball(s) -->
<target name="tar" depends="package, deploy-contrib">