fixed #2280 fixed a bug that need not deleteBuffer in onExit
Merge branch 'develop' of https://github.com/cocos2d/cocos2d-html5 into Iss2280_FixVideoMomeryBug
Merge pull request #984 from dingpinglv/Iss2280_FixVideoMomeryBug

fixed #2280 fixed a bug that needn't call deleteBuffer in onExit