Add Java to deb dependencies.

I fired up a fresh Linode, grabbed and installed the deb from the website, and ran `invoke-rc.d riemann start`. It returned with an exit code of 0, so I assumed all was well.

It wasn't!

I eventually tracked the issue down. I didn't have Java installed. It'd have been nice if `dpkg` had bailed, telling me that what I needed.

I've added the same Java dependency that the Debian/Ubuntu Clojure package uses:

http://bazaar.launchpad.net/~ubuntu-branches/ubuntu/raring/clojure1.4/raring/view/head:/debian/control#L17

Test plan: `lein fatdeb` still works...