Ignore Paxos commits for truncated tables

patch by Sam Tunnicliffe; reviewed by Aleksey Yeschenko for
CASSANDRA-7538
Merge branch 'cassandra-2.0' into cassandra-2.1

Conflicts:
	CHANGES.txt
	src/java/org/apache/cassandra/service/paxos/PaxosState.java
Merge branch 'cassandra-2.1' into trunk