preload audio resource
Merge remote-tracking branch 'cocos2d-html5/master' into issue1569_audioJSB
Merge remote-tracking branch 'cocos2d-html5/master' into issue1569_audioJSB
Merge remote-tracking branch 'cocos2d-html5/master' into issue1569_audioJSB
audio bug
Merge remote-tracking branch 'cocos2d-html5/master' into issue1569_audioJSB