Catch memtable flush exceptions during shutdown
patch by Sergio Bossa; reviewed by jbellis for CASSANDRA-6735
merge from 1.2
Merge branch 'cassandra-2.0' into cassandra-2.1
Merge branch 'cassandra-2.1' into trunk
Return an empty meta object instead of None.
Patch by Mikhail Stepura; reviewed by Brandon Williams for CASSANDRA-6741
Merge branch 'cassandra-2.1' into trunk