Allow Kafka brokers without port definition.

If the kafka catalog file contains brokers without a port specified,
use the default Kafka port (9092).
Fix NPE if key or message are absent.

If no key or message was ever collected, the Kafka API actually
returns null for key() or payload(). Deal with this case correctly.
Force newer snappy version used by Kafka

This fixes all problems seen with
https://github.com/xerial/snappy-java/issues/17 on e.g. CentOS 5 by
replacing the included library version 1.0.5 with the latest version
as suggested by xerial.

This is proposed to go into Kafka proper, see
https://issues.apache.org/jira/browse/KAFKA-1369
Fix HashAggregation infinite loop during multiple partial agg flushes