Preserves CQL metadata when updating table from thrift

patch by mishail; reviewed by iamaleksey & slebresne for CASSANDRA-6831
Merge branch 'cassandra-1.2' into cassandra-2.0

Conflicts:
	src/java/org/apache/cassandra/thrift/CassandraServer.java
Merge branch 'cassandra-2.0' into cassandra-2.1

Conflicts:
	CHANGES.txt
	src/java/org/apache/cassandra/config/CFMetaData.java
	test/unit/org/apache/cassandra/config/CFMetaDataTest.java