Bump Cassandra version for tests to 2.1.0-rc7.
Update tests for new frozen<> CQL keyword (JAVA-441).
Expose "frozenness" on DataType (JAVA-441).
Add @Frozen mapping annotations (JAVA-441).
Check @Frozen annotations in mapper (JAVA-441).
Merge pull request #221 from olim7t/java441

Take into account new "frozen" attribute