title: postgresql migrating JSON to JSONB
body: <p>In postgresql 9.4 the new JSONB was incorporated.  </p>
  
  <p>On a live DB in postgresql 9.3 I have a JSON column.  </p>
  
  <p>I want to migrate it to JSONB.  </p>
  
  <p>Assuming I migrated the DB first to 9.4 (using pg_upgrade). What do I do next?</p>