Fix DISTINCT on static columns with paging

Patch by Tyler Hobbs; reviewed by Sylvain Lebresne for CASSANDRA-8087
Merge branch 'cassandra-2.0' into cassandra-2.1

Conflicts:
	CHANGES.txt
	src/java/org/apache/cassandra/cql3/statements/ColumnGroupMap.java
	src/java/org/apache/cassandra/db/DataRange.java
	src/java/org/apache/cassandra/db/PagedRangeCommand.java