Fix hint replay with many accumulated expired hints

patch by Aleksey Yeschenko; reviewed by Jonathan Ellis for
CASSANDRA-6998
Merge branch 'cassandra-2.0' into cassandra-2.1

Conflicts:
	CHANGES.txt
	src/java/org/apache/cassandra/db/HintedHandOffManager.java
Merge branch 'cassandra-2.1' into trunk