Fixed retina/contentScale position errors for iPhone 6+ devices in EditBox.

Problem is that factor was 1.0 or 2.0 until iOS 8 introduced 3.0.
Merge pull request #1 from cocos2d/v3

Update from cocos2d-x
async task pool
Merge branch 'v3' of https://github.com/cocos2d/cocos2d-x into v3
Merge branch 'v3' of https://github.com/cocos2d/cocos2d-x into v3
add createAsync
Merge branch 'v3' of https://github.com/cocos2d/cocos2d-x into v3
let billboard can rotate in the Z axis
add async task callback dipatcher, call it in the main thread
add async load test
fix ~ThreadTasks() bug
Remove useless copy about luasocket on the android platform
modify async load sample
refactor async load callback funtion
add comment
modify comment
createAsync comment
correct unsuitable word
update for cocos reader
ListViewReader completed and listview callback feature.