Fix MS expiring map timeout for CAS messages

patch by kohlisankalp; reviewed by slebresne for CASSANDRA-7752
Merge branch 'cassandra-2.0' into cassandra-2.1.0

Conflicts:
	CHANGES.txt
	src/java/org/apache/cassandra/config/DatabaseDescriptor.java
Merge branch 'cassandra-2.1.0' into cassandra-2.1
Merge branch 'cassandra-2.1' into trunk