backport CASSANDRA-6927 to 2.0
merge
Merge branch 'cassandra-2.1' into trunk
Fix NPE at compaction leftover cleanup for dropped table

patch by yukim; reviewed by jbellis for CASSANDRA-7770
Merge branch 'cassandra-2.1.0' into cassandra-2.1
Merge branch 'cassandra-2.1' into trunk
Fixed the error when tracing query with cqlsh

patch by Robert Stupp; reviewed by Mikhail Stepura for CASSANDRA-7613
Merge branch 'cassandra-2.1' into trunk
Merge remote-tracking branch 'origin/trunk' into 7562-udf-java