Handle CQL row marker in SSTableImport

patch by Mikhail Stepura; reviewed by Tyler Hobbs for CASSANDRA-7477
Merge branch 'cassandra-2.1.0' into cassandra-2.1

Conflicts:
	test/unit/org/apache/cassandra/tools/SSTableImportTest.java
Merge branch 'cassandra-2.1' into trunk

Conflicts:
	test/unit/org/apache/cassandra/tools/SSTableImportTest.java