premultiplied alpha for PNG,TGA,WEBP,RAW_DATA
no need for handling RAW_DATA
we are only udpating PNG now.
[ci skip]
fix scale9Sprite can't culling problem
add test case to break buggy code
Merge pull request #6957 from andyque/fixScale9Sprite

fix scale9Sprite can't culling problem
[ci skip]
fixed EVENT_COME_TO_BACKGROUND has not been sent on android.
Merge pull request #6958 from Dhilan007/v3

fixed EVENT_COME_TO_BACKGROUND has not been sent on android.
[ci skip]
[ci skip]
bugfix related to AutoreleasePool's PoolManager

* duplicated AutoreleasePool added to PoolManager in
  PoolManager::getInstance()
* redundant pop_back() in PoolManager::~PoolManager()
remove unnecessary cache-variable
prefer std::vector to other containers
not treat warnings as error
Merge pull request #6961 from minggo/treat-warning-as-error

not treat warnings as error
Merge pull request #6954 from visiblelight/AlphaIssues

Make PNG files premultiplied alpha when loading
[ci skip]
remove sortChildren of Layout