fix Value's memory leak
add destroyInstance for ScriptHandlerMgr
delete _scriptHandlerMgr in destruct will cause stack overflow
Update RELEASE_NOTES.md
Fixed a bug where an event listener removed from the event dispatcher while it is still in the _toAddedListeners vector would never have _isRegistered set to false on removal. This causes it to fail an assert if it is attempted to be added to the event dispatcher again later.
Merge pull request #6157 from dbaack/remove_event_listener_fix

closed #4700: Removing and re-adding an event listener will trigger an assert.
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Merge pull request #6156 from zakmandhro/patch-1

A typo fix in RELEASE_NOTES.md
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Merge pull request #6150 from mgcL/Value-memory-leak

A potential memory leak in value's default constructor.
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CCEventDispatcher crash fix
Fix possible crashes which could be caused by the EventDispatcher having listeners associated with nodes are destroyed. Catch the case where a node registers a listener while we are dispatching events and gets destroyed while that event is still being dispatched. Check the list of nodes to be added into the event dispatcher fully when we are cleaning listeners for a target node.

This issue was found using the extra debug verification in this pull request:
https://github.com/cocos2d/cocos2d-x/pull/6011
Add an event dispatcher test
Add an event dispatcher test to help reproduce crashes fixed by the previous commit and to verify that the fix still works.
Add extra CCNode verification
Add a check to the CCNode destructor to catch a common cocos2d-x programming mistake - forgetting to call base class onExit() in derived class onExit() implementations. We can check for this invalid API usage by checking if the node is still marked as running on destruction. If the node still thinks it's running then it's likely the cleanup logic performed by Node::onExit() was not done.
Unregistered listener when it's removed from _toAddedListeners.
Merge pull request #6162 from dumganhar/pull/6160

Fixed a potential crash in EventDispatcher, based on PR #6160
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