Make the CL native protocol code match the on in 2.0

patch by slebresne; reviewed by jasobrown for CASSANDRA-6347
Merge branch 'cassandra-1.2' into cassandra-2.0

Conflicts:
	src/java/org/apache/cassandra/db/ConsistencyLevel.java
Merge branch 'cassandra-2.0' into trunk
SSTable/SSTableReader cleanup

patch by yukim; reviewed by jbellis for CASSANDRA-6355