Fix failing pig test

Patch by Alex Liu, reviewed by brandonwilliams for CASSANDRA-6376
Merge branch 'cassandra-1.2' into cassandra-2.0
Fix truncate to not abort due to unreachable fat clients
patch by Oleg Anastasyev; reviewed by jbellis for CASSANDRA-6864
Merge remote-tracking branch 'origin/cassandra-2.0' into cassandra-2.0
Log more information when exceeding tombstone_warn_threshold
patch by Oleg Anastasyev; reviewed by jbellis for CASSANDRA-6865