support destroyScheduler
support ayncCloseConnectionEnable
bug fixed for support create/destroy scheduler
Merge pull request #615 from wenshao/master

support create/destory scheduler
bug fixed for clone
bug fixed for getHoldable UnsupoortedOperationException
Merge pull request #617 from wenshao/master

bug fixed for clone
bug fixed for create/destroy scheduler & add testcase
Merge pull request #618 from wenshao/master

bug fixed for create/destroy scheduler & add testcase
Merge pull request #619 from yakolee/master

improve sqlwall