Continue with assassinate even if the endpoint vanishes during the
sleep-for-safety check.

Patch by brandonwilliams, reviewed by Jeremiah Jordan for CASSANDRA-6787
Merge branch 'cassandra-1.2' into cassandra-2.0
Merge branch 'cassandra-2.0' into cassandra-2.1
Merge branch 'cassandra-2.1' into trunk
Lock counter cells, not partitions

patch by Aleksey Yeschenko; reviewed by Benedict Elliott Smith for
CASSANDRA-6880
Merge branch 'cassandra-2.1' into trunk
Fix BTree.clear for large updates
patch by Benedict Elliott Smith; reviewed by jbellis for CASSANDRA-6943
merge from 2.1
Fix bad merge of 6825 into cassandra-2.1

Patch by Tyler Hobbs; reviewed by Aleksey Yeschenko for CASSANDRA-6978
Merge branch 'cassandra-2.1' into trunk
Fix SSTable not released if stream session fails

patch by yukim; reviewed by Richard Low for CASSANDRA-6818
Merge branch 'cassandra-2.0' into cassandra-2.1
Merge branch 'cassandra-2.1' into trunk
fix test compile
Merge branch 'cassandra-2.1' into trunk