Fix deletion for indexes on primary key columns

patch by slebresne; reviewed by thobbs for CASSANDRA-8206
Merge branch 'cassandra-2.0' into cassandra-2.1

Conflicts:
	CHANGES.txt
	src/java/org/apache/cassandra/db/index/AbstractSimplePerColumnSecondaryIndex.java
	src/java/org/apache/cassandra/db/index/PerColumnSecondaryIndex.java
	src/java/org/apache/cassandra/db/index/SecondaryIndexManager.java