Emit metrics for CAS

Patch by Sankalp Kohli, reviewed by brandonwilliams for CASSANDRA-7341
Merge branch 'cassandra-2.0' into cassandra-2.1
Emit metrics for CAS

Patch by Sankalp Kohli, reviewed by brandonwilliams for CASSANDRA-7341
Merge branch 'cassandra-2.1' into trunk

Conflicts:
	src/java/org/apache/cassandra/service/paxos/PaxosState.java
Emit metrics for CAS

Patch by Sankalp Kohli, reviewed by brandonwilliams for CASSANDRA-7341
Merge branch 'cassandra-2.0' into cassandra-2.1
Merge branch 'cassandra-2.1' into trunk