Make StreamReceiveTask thread safe and gc friendly

patch by yukim; reviewed by benedict for CASSANDRA-7795
Merge branch 'cassandra-2.0' into cassandra-2.1.0

Conflicts:
	CHANGES.txt
	src/java/org/apache/cassandra/streaming/StreamReceiveTask.java
Merge branch 'cassandra-2.1.0' into cassandra-2.1