IN on the last clustering columns + ORDER BY DESC yield no results

patch by slebresne; reviewed by thobbs for CASSANDRA-6701
Merge branch 'cassandra-1.2' into cassandra-2.0

Conflicts:
	src/java/org/apache/cassandra/cql3/statements/SelectStatement.java
Merge branch 'cassandra-2.0' into trunk

Conflicts:
	src/java/org/apache/cassandra/cql3/statements/SelectStatement.java
Lift limitation that order by columns must be selected for IN queries

patch by slebresne; reviewed by thobbs for CASSANDRA-4911