Better support for CAS primitives (e.g. INSERT ... IF NOT EXISTS)

[kilograham]

This seems to require v2 of the protocol just from looking at the C* side code.

I'd suggest that all update queries return a boolean, which is always true for non conditional updates.

Using prepared statements currently throws an assertion failure, because a result is given but not expected

here is the code from the server side for the result

    ColumnSpecification spec = new ColumnSpecification(ksName, cfName, CAS_RESULT_COLUMN, BooleanType.instance);
    ResultSet.Metadata metadata = new ResultSet.Metadata(Collections.singletonList(spec));
    List<List<ByteBuffer>> rows = Collections.singletonList(Collections.singletonList(BooleanType.instance.decompose(success)));

where CAS_RESULT_COLUMN is "[applied]"