Migrate key_alias->key_aliases on every schema migration (1.2)

Another follow-up to 5800
Merge branch 'cassandra-1.2' into cassandra-2.0.0
Merge branch 'cassandra-2.0.0' into cassandra-2.0
Added lines for BATCH response to v2 spec
Merge branch 'cassandra-2.0.0' into cassandra-2.0
Merge branch 'cassandra-2.0' into trunk