Hint streaming can cause decommission to fail

patch by jasobrown, reviewed by marcuse for CASSANDRA-7219
Merge branch 'cassandra-1.2' into cassandra-2.0

Conflicts:
	CHANGES.txt
	src/java/org/apache/cassandra/service/StorageService.java
Merge branch 'cassandra-2.0' into cassandra-2.1

Conflicts:
	CHANGES.txt