Prevents calls to setAutoCommit that don't change the auto-commit state

Calls to setAutoCommit always set it as a dirty attribute, even if they don't effectively change auto-commit state. This will cause another call to setAutoCommit when returning the connection to the pool.

Some drivers don't do well with calls to setAutoCommit when in transaction. This change will prevent those calls (as long as it's set to false in the configuration).