Fix CAS conditions for COMPACT STORAGE tables

patch by slebresne; reviewed by iamaleksey for CASSANDRA-6813
Merge branch 'cassandra-2.0' into cassandra-2.1

Conflicts:
	CHANGES.txt
	src/java/org/apache/cassandra/cql3/ColumnCondition.java
	src/java/org/apache/cassandra/cql3/statements/CQL3CasConditions.java