ps2 protocol for INSERT/UPDATE/DELETE

there's a way to make ps2 protocol to work for INSERT/UPDATE/DELETE.

It could work approximately like this

• when mariadb-test gets an INSERT/UPDATE/DELETE to execute:
  • prepare the statement
  • if SERVER_STATUS_IN_TRANS
    • execute (simple ps1 protocol)
  • otherwise
    • run START TRANSATION
    • execute (ps2 step 1)
    • if SERVER_STATUS_IN_TRANS is not set
      • run COMMIT or ROLLBACK — it was non-transactional table
    • otherwise
      • run ROLLBACK
      • execute ps2 step 2

this isn't perfect, won't wok for multi-update/delete that accesses both transactional and non-transactional tables. They are rare and will have to be protected with disable_ps2_protocol.

also it's possible to make it work when not autocommit — with savepoints.