Add proper compare function for CollectionType (for UDT sake)

patch by slebresne; reviewed by thobbs for CASSANDRA-6783
Merge branch 'cassandra-2.1' of https://git-wip-us.apache.org/repos/asf/cassandra into cassandra-2.1

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