a potential bug in Layer.

https://github.com/cocos2d/cocos2d-x/issues/2948
Update CCLayer.cpp

change "_accelerometerEnabled = false"
to "setAccelerometerEnabled(false)"
in method init().
a potential bug in ScrollView

check _touches in setTouchEnabled
Merge pull request #2950 from zcgit/develop

a potential bug in Layer.