Account for range tombstones in min/max column names

Patch by Oleg Anastasyev, reviewed by marcuse for CASSANDRA-7235
Merge branch 'cassandra-2.0' into cassandra-2.1

Conflicts:
	CHANGES.txt
	src/java/org/apache/cassandra/db/ColumnFamily.java
	src/java/org/apache/cassandra/db/compaction/LazilyCompactedRow.java