cassandra module only with 1.7

git-svn-id: https://svn.apache.org/repos/asf/archiva/trunk@1543702 13f79535-47bb-0310-9956-ffa450edef68
start some perf improvement for cassandra

git-svn-id: https://svn.apache.org/repos/asf/archiva/trunk@1543703 13f79535-47bb-0310-9956-ffa450edef68