Fix native protocol CAS batches

patch by Sylvain Lebresne; reviewed by Aleksey Yeschenko for
CASSANDRA-7337
Merge branch 'cassandra-2.0' into cassandra-2.1

Conflicts:
	CHANGES.txt
	src/java/org/apache/cassandra/cql3/QueryProcessor.java
	src/java/org/apache/cassandra/cql3/statements/BatchStatement.java
	src/java/org/apache/cassandra/transport/messages/BatchMessage.java