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
if relocate is a no-op, don't try to op.
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
Add missing CHANGES.txt entry for CASSANDRA-6933
Revert "Fix LatencyMetrics returning infinity."

This reverts commit 5e51aa4e6d1d868bb82a1aa2ffaed4613b24ffc1.
getRecentLatency returns zero instead of infinity

Patch by Benedict, reviewed by brandonwilliams for CASSANDRA-6920
Merge branch 'cassandra-2.0' into cassandra-2.1
Revert "Fix LatencyMetrics returning infinity."

This reverts commit 5e51aa4e6d1d868bb82a1aa2ffaed4613b24ffc1.
getRecentLatency returns zero instead of infinity

Patch by Benedict, reviewed by brandonwilliams for CASSANDRA-6920
Merge branch 'cassandra-2.1' into trunk
Track presence of legacy counter shards in sstables

patch by Aleksey Yeschenko; reviewed by Marcus Eriksson for
CASSANDRA-6888
Merge branch 'cassandra-2.1' into trunk
Ensure safe resource cleanup when replacing SSTables

Patch by belliotsmith; reviewed by Tyler Hobbs for CASSANDRA-6912
Merge branch 'cassandra-2.1' into trunk