Enable RELEASE SAVEPOINT to execute within a transaction

[hymkor]

English

• Fix: Errors were not reported during execution of SAVEPOINT and SAVE TRANSACTION.
• Enable RELEASE SAVEPOINT to execute within a transaction

Japanese

• SAVEPOINT, SAVE TRANSACTION の実行中にエラーが発生してもメッセージが表示されなかった問題を修正
• RELEASE SAVEPOINT もトランザクション内で実行できるようにした。