Making dropwizard-extra-kafka work with Kafka 0.7.2

Hi,

This pullrequest contains some small changes to make dropwizard-extra-kafka work with Kafka 0.7.2  which is the latest stable version here: http://kafka.apache.org/downloads.html

I use scala 2.8.0 since this is the same version as found in Kafka source.

I've deployed kafka to my local repo, by using

    ./sbt make-pom

and some copying :) 

I hope you can pull it or upgrade to 0.7.2 in some other way