Fix Assertion errors when using empty clustering with static columns

patch by slebresne; reviewed by iamaleksey for CASSANDRA-7455
Merge branch 'cassandra-2.0' into cassandra-2.1.0

Conflicts:
	CHANGES.txt
	src/java/org/apache/cassandra/db/compaction/LeveledManifest.java
Merge branch 'cassandra-2.1.0' into cassandra-2.1

Conflicts:
	CHANGES.txt
	src/java/org/apache/cassandra/db/compaction/LeveledManifest.java
Merge branch 'cassandra-2.1' into trunk
Merge branch 'cassandra-2.0' into cassandra-2.1.0

Conflicts:
	src/java/org/apache/cassandra/cql3/statements/ColumnGroupMap.java
Merge branch 'cassandra-2.1.0' into cassandra-2.1
Merge branch 'cassandra-2.1' into trunk
typo
Merge branch 'cassandra-1.2' into cassandra-2.0

Conflicts:
	CHANGES.txt
Merge branch 'cassandra-2.0' into cassandra-2.1.0
Merge branch 'cassandra-2.1.0' into cassandra-2.1
Merge branch 'cassandra-2.1' into trunk
Split out outgoing stream throughput within a DC and inter-DC
patch by Vijay and benedict for CASSANDRA-6596
Merge branch 'cassandra-2.0' into cassandra-2.1.0
rename
Merge branch 'cassandra-2.1' into trunk
Upgrade to snappy-java 1.0.5.2
Merge branch 'cassandra-2.1.0' into cassandra-2.1
Merge branch 'cassandra-2.1' into trunk
Make sure cql-test only run CQLTester ones