If a batch fails because of an unprepared statement, reprepare the statement and redo the batch.
Replace case that was made invalid when error structs were exposed to conn.executeQuery for ErrUnprepared.
Add tests to ensure queries are re-prepared
Use Pool.Pick() rather than Node.Pick()
Refactor reprepare statement tests
Merge pull request #168 from ChannelMeter/reprepare_cass2_batchv2

Reprepare cassandra 2.x style batch if batch fails due to unprepared statement