Fix prepared statement on thrift post-6659
Fix Cassandra 2.0.x validates Thrift columns incorrectly

patch by thobbs and slebresne; reviewed by thobbs and slebresne for CASSANDRA-6892
Fix error with super columns in mixed 1.2-2.0 cluster

patch by slebresne; reviewed by iamaleksey for CASSANDRA-6966
Fix bad skip of sstables on slice query with composite start/finish

Patch by Tyler Hobbs; reviewed by Sylvain Lebresne for CASSANDRA-6825