Use Cassandra 1.2.6

Cassandra 1.2.6 uses snappy-java 1.0.5 instead of 1.0.4.1.
snappy java 1.0.4.1 has problem on Java 7 environment.
https://github.com/ptaoussanis/carmine/issues/5
Merge pull request #109 from ledmonster/use-cassandra-1.2.6

Use Cassandra 1.2.6