Throw IRE for relations on entire collections

Patch by Tyler Hobbs; review by Sylvain Lebresne for CASSANDRA-7506
Merge branch 'cassandra-2.0' into cassandra-2.1.0
Merge branch 'cassandra-2.0' into cassandra-2.1

Conflicts:
	CHANGES.txt
Merge branch 'cassandra-2.1.0' into cassandra-2.1